SANA'A - Authorities have detained a total of 20 people in connection with an attack last month on the French oil tanker Limburg, security officials said Wednesday.
Those detained included two watchmen from the house rented by the suspected perpetrators of the attack on the Limburg, the officials said on condition of anonymity.
Other detainees included three people who transported a boat used in the attack from the house to the shore.
The officials said the main suspects in the attack were still at large.
Meanwhile, the bulk of the official investigation into the Limburg blast is over, and the ship has been pulled to waters in Fujairah, United Arab Emirates. It was attacked by a small explosives-laden boat off Yemen's coast on Oct. 6. One Bulgarian crewman died and about 90,000 barrels of crude oil spilled into the Arabian Sea.
Earlier this month, Yemeni Prime Minister Abdul-Kader Bajammal said the attack was similar to the 2000 bombing of the USS Cole and might have been carried out by the same group.
The United States blames Osama bin Laden's al-Qaida for the suicide attack on the Cole while the ship was refueling in the southern port of Aden. Yemen is yet to set a date for the trial of at least six people arrested in the Cole investigation, and so far hasn't directly linked the attack to al-Qaida.
A U.S. intelligence official in Washington has said U.S. experts believed the Limburg attack was carried out by people linked to al-Qaida.
Two statements last week attributed to bin Laden and al-Qaida hailed the attack on the Limburg but didn't claim responsibility.
Officials have said the boat used in the attack was bought from outside Yemen and transported by land into the country.

An official of Yemen's ruling GPC party, and former intelligence official, is being held in Egypt after being "kidnapped" with the help of Egypt's ambassador to Yemen, according to the victim's brother.
Abdul Wahab Ali Abdul Rahman, brother of Abdul Salaam Ali Abdul Rahman, a member of the Central Committee of the ruling General People's Congress in Yemen, said that Egypt's ambassador to Yemen Khaled al-Koumi "dragged his brother into a trap installed by the Egyptian intelligence ."
Rahman has also accused Egyptian intelligence of the kidnapping his brother, who disappeared in Egypt September 20
This week Saba, the Yemeni official news agency, confirmed the GPC official is being held by Egyptian authorities.
Rahman, who is a businessman involved with biding contracts, said he believes his brother is being held by Egyptian intelligence for information about Afghani Arabs in Yemen.
An unidentified source close to the Yemeni government said the missing man has had been active agent for the Yemeni intelligence and helped Yemeni government to extradite thousands of Arab Afghans from Yemen including Egyptians.
Saba News Agency said the Yemeni cabinet agreed in a meeting this week to follow up on the disappearance of the Yemeni citizen.
There are conflicting reports of where he may be at this time.
His brother, Abdulwahab, accuses not only the Egyptian ambassador to Yemen, but also Arab Contractors Company of presenting him to the Egyptian intelligence, by inviting him to Cairo.
But the Egyptian ambassador denied such allegations and said the Yemeni citizen left Cairo for another country.
And the news agency Saba has also quoted the Yemeni interior and foreign minister office of the interior and the foreign minister as saying Rahman left Cairo on board of a private plane to Baku, capital of Azerbaijan, four days after his arrival in Cairo.
Some sources said the missing Yemen man might have been extradited to the US but this has not been confirmed.
Political observers have not dismissed the idea that he might have been a victim of a political bargain among Yemen, Egypt and the US.
Abdul Salaam is believed to have important information on Arab Afghans who have been extradited from Yemen which should be useful for the US in its war on terrorism.
Abdul Wahab, 28, says his elder brother Abdul Salaam, 34, is married and the father of four children.
He says that he has met with the Egyptian ambassador and the Egyptian consul in Sanaa in search for his brother for several times, and Egyptian officials maintain his brother Abdul Salaam has left Cairo just and was "heading for Baku."
Sources from the Abdulrahaman family, however, say that he is still in Egypt.
Yemen's government has stressed that security and judicial agreements signed with Egypt should be respected.
Abdulwahab accused the office of the Arab Contractors Company in Sana'a of being involved in the arrest of his brother in Cairo.
He said he and his tribe will sue the Arab Contractors Company employees of Egyptian nationality, and he's asked the General Prosecutor not to let them leave Yemen until his brother's whereabouts is known.
He said he received a call from the consultant of the Arab Contractors Company in Cairo, Mustafa Khaleel who told him his brother is safe but he will not be able to talk to his family at the moment.
He said his brother is one of the stakeholders of the company branch in Yemen and that a misunderstanding between him and other people in the company took place some time ago but the difference was sorted out.
The tribe Bani Hushaish appealed in a press statement last Thursday to the government of Yemen and all human rights organization to exert more efforts to get their man back.
They said any harm against him would be a violation against Yemen's sovereignty and all its people.
Close sources from his family said when al-Hilah left Yemen for Cairo; he already booked for his return to Yemen, having no plan to go to any other country.
He informed his family after his arrival in Cairo that he met the Arab Contractors Company chief and his talks with him were positive.
The sources said he was received at Cairo airport by Mustafa Khaleel and other three people who were said later they were members of the Egyptian intelligence.
They are Husam Khawrasheed, Hasan Duwaidat, and another one named in part, Lashtin, who has been said to have visited Yemen several times as a businessman. He met some Yemeni businessmen with the purpose of bringing some Egyptian companies to carry out some projects.

A Yemeni was killed after unidentified armed tribesmen launched an attack on the house of a well-known tribal sheikh here early yesterday.
The Gulf News reported this week that the "gunmen bombarded the upper part of the two-storey house with rocket-propelled grenade projectile late at night. The sheikh's bodyguards chased the attackers and killed one of them."
The house is located in the heart of a residential complex belonging to Shiekh Abdul Azeez Al Shaif in the northern suburb of Sanaa.
Shiekh Al Shaif, chief of the Bakil tribe, the second largest tribe in Yemen, told reporters after the attack that Al Qaeda was behind the assault.
"Terrorist elements affiliated to Al Qaeda Organization targeted my house because of my cooperation with the authorities in pursuing them," he said.
However, officials ruled out Al Qaeda was behind the attack, saying that it was only an act of revenge act between the Al Shaif tribe and another from Barat district.
Tribal sources told Gulf News that the supporters of Shiekh Al Shaif were blockading the tribe of Al Ashabi in Barat district, the tribe of the attackers.
Two weeks earlier, armed men attacked Al Shaif's other house in Al Jawf province, 170km east of Sanaa. Windows of the targeted house were broken and a gaping hole left in the wall of one bedroom, an AFP correspondent reported.
The family of the Sheikh's son Mohammad, an MP and chairman of parliament's human rights committee, occupies the building in the compound.
U.S. military personnel have been deployed in Yemen to help Sanaa crack down on suspected militants of the Al Qaeda terror network in the wake of the September 11, 2001, suicide hijackings in the United States.
The family of Saud-born Al Qaeda chief Osama bin Laden hails from Yemen.
Clashes involving tribes are common and often bloody in Yemen, where the number of firearms in civilian hands is officially estimated at more than 60 million, or more than three per inhabitant.
Meanwhile, a tribal source told The Yemen Times that al-Qaeda members are not behind the attack. "The attackers belong to the al-Qasemi and Ashaef tribes where the Shiekh belongs to," the source added.
Ashaef told The Yemen Times earlier that the attackers are of al-Qaeda members. The Shiekh cooperated with the authorities to hand over al-Qaeda suspects such as Abu Abdurahman al-Jazaeri.
Official source at the interior ministry said that the reason behind the attack was due to criminal motives and that the al-Qaeda members have no links with such attacks.