US officials said Tuesday the deadly attack on a US consulate in Libya has prompted a renewed focus on the threat posed by Al-Qaeda's affiliate in North Africa, suspected of possible links to last month's assault.

Precisely who was behind the September 11 attack that killed the US ambassador to Libya and three of his staff remains under investigation but Al-Qaeda in the Islamic Maghreb is now under intense scrutiny given its possible role in the incident, two officials said.

"Obviously there's a spike of interest in AQIM since the attack," an administration official told AFP.

The US government's probe of the assault is "looking at extremist groups in the Benghazi area as well as AQIM," said the official, who spoke on condition of anonymity.

"It doesn't appear at this point that there was a highly organized command and control structure but it was nonetheless a relatively complex attack," the official said.

The Al-Qaeda franchise called on Muslims to storm other US embassies in North Africa and kill American envoys days after the assault on the Benghazi mission, in which gunmen kept security teams at bay for hours and fired rocket-propelled grenades.

In the past, US spy agencies have portrayed AQIM as a lesser threat than some other branches of Al-Qaeda, with the group not yet able to carry out plots on targets overseas like its counterparts in Yemen or Pakistan.

But US officials have been concerned that the fall of dictator Moamer Kadhafi in Libya created more room for extremists like AQIM to operate, while also freeing up weapons.

"It's definitely getting more attention," said a second US official, who spoke on condition of anonymity.

Just the possibility that AQIM may have played a role in the Benghazi attack has concentrated the spotlight on the outfit, the official added.

The Washington Post reported Tuesday that the United States may expand its campaign of drone strikes against Al-Qaeda to target the desert bases of AQIM.

A spokesman for President Barack Obama's National Security Council would not confirm details of an internal debate among the CIA, the State Department and the Pentagon.

But NSC spokesman Tommy Vietor told AFP: "The president has been clear about his goal to destroy Al-Qaeda's network and we work toward that goal every day.

"It shouldn't come as a surprise that the White House holds meetings on a variety of subjects, including a number of counterterrorism issues," he added.

AQIM was already taking on greater importance in Washington after having seized large swaths of Mali and taking control of weapons from post-revolutionary Libya.

The top US diplomat for Africa, Johnnie Carson, told journalists on Monday that the United States would be open to supporting a "well planned" and "well resourced" African-led force to help oust Islamist rebels in northern Mali.