The suicide squad that assaulted the U.S. embassy in Yemen in September had links to al-Qaida and some even had fought in Iraq, a Yemeni security official said Saturday.
The official added that the United Nations has raised its security level in Yemen in response to terrorist threats.
The six Yemeni men who carried out the Sept. 17 attack against the gates of the U.S. embassy were trained at al-Qaida camps in the southern Yemeni provinces of Hadramut and Marib and three of them had recently returned from Iraq, the official added.
The official spoke on condition of anonymity because he wasn't authorized to speak to the press.
Armed with rocket propelled grenades and assault rifles, the attackers drove two cars packed with explosives into the embassy gate and sprayed it with bullets before being killed. Aside from the attackers, 13 others died in the incident, including an 18-year-old American woman of Yemeni origin.
It was the deadliest direct assault on a U.S. Embassy in a decade.
The U.S. counts Yemen as an ally in the war on terrorism. But American officials have long been frustrated over what is seen as a "revolving door" policy toward al-Qaida militants by President Ali Abdullah Saleh's government.
Yemen has let some convicted militants go free after promising to refrain from violence.
While U.N. officials would not confirm whether there have been any threats against them, on Oct. 18 the international organization increased its security level to "phase 3," which means family members and essential staff have to leave the country.
"The U.N. Secretary General has temporarily increased the security level to phase 3 purely as an internal precautionary measure," resident coordinator Pratibha Mehta said in a statement. "U.N. essential staff will remain and we will continue to implement all UN programs and operations."
Yemeni Foreign Minister Abu-Bakr al-Qirbi has held a meeting with western ambassadors to assure them that Yemeni authorities have taken necessary security measures to secure their missions in the country, said a ministry statement.
Car bomb factory
Yemeni Interior Minister Mouthar al-Masri also announced that authorities have uncovered a factory for building car bombs, without giving the location of the factory.
For years, the government has let some al-Qaida figures and other Islamic extremists go free in political deals hoping to keep them quiet.
But the policy of compromise may be falling apart with the return of younger radicals who fought alongside al-Qaida in Iraq, but left after the group was heavily squeezed by the U.S. military and Sunni tribes there.
Yemen has seen an upswing of attacks that security officials say likely involved Iraq veterans. In July 2007, for example, a suicide bomber detonated his car among tourists at an ancient temple in central Yemen, killing seven Spaniards and two Yemenis. There have also been reported attacks on Yemen's large Muslim minority sects, the Zaydis and Shiites, seen as heretics by Sunni extremists.