WASHINGTON - The State Department made a " grievous mistake" in keeping the US consulate in Benghazi of Libya open despite insufficient security before it was attacked on September 11, a Senate committee said in a report on Monday.

"Despite the inability of the Libyan government to fulfill its duties to secure the facility, the increasingly dangerous threat assessments, and a particularly vulnerable facility, the Department of State officials did not conclude the facility in Benghazi should be closed or temporarily shut down," said the report compiled by the Senate Homeland Security Committee.

"That was a grievous mistake," it concluded.

The report faulted the State Department for not beefing up security of the US mission despite increasingly alarming security risks assessment.

It also noted that the lack of specific threats warning for the Benghazi consulate may reflect a "failure" by the US intelligence community to pay enough attention to militant groups that is not directly linked to al-Qaida.

The report therefore recommended that the US intelligence apparatus "broaden and deepen their focus in Libya and beyond, on nascent violent Islamist extremist groups in the region that lack strong operational ties to core al Qaeda or its main affiliate groups."

On December 18, the independent Accountability Review Board (ARB) had already released a review of the Benghazi attack. The report found that "management deficiencies" at high levels of the State Department had contributed to the deadly outcome.

The deadly September 11 attack in the eastern Libyan city of Benghazi killed US ambassador to Libya Christopher Stevens and three other Americans.

Following the ARB report, four State Department officials were removed from their posts, including Eric Boswell, assistant secretary of state for diplomatic security.

President Barack Obama said on Sunday that he would not dispute the findings of the recent probe that showed a "huge problem" in security management in the US consulate in Benghazi.