The United States will have to keep up an open-ended drone war against al-Qaida militants in Pakistan and elsewhere to prevent another terror attack on America, Defense Secretary Leon Panetta said.

The assassination of al-Qaida figures in Pakistan, Yemen and Somalia with unmanned, robotic aircraft has provoked widespread criticism from human rights groups and some U.S. allies, but Panetta said the U.S. campaign has been effective.

At least six people were killed when a suicide bomber blew himself up amongst a group of security officials outside the Somali prime minister's office on Tuesday, army officials said.

"I saw the dead bodies of six people and several others were injured," said Abdukadir Ali, a Somali military official who stayed near the scene of the attack in central Mogadishu.

Twitter suspended the account of Somalia's Al-Qaeda linked Shebab insurgents Friday, days after they posted photographs of a French commando they killed and threatened to execute Kenyan hostages.

A message from Twitter on the English-language @HSMPress account read that it had "been suspended", without elaborating. The extremist's Arabic account confirmed the suspension, denouncing it as censorship.

The United States and Somalia on Thursday launched a new era of diplomatic relations, as Washington recognized the African nation's government for the first time since 1991.

"Today is a milestone. It is not the end of the journey, but it is an important milestone towards that end," U.S. Secretary of State Hillary Clinton said after talks with new Somali President Hassan Sheikh Mohamoud.

Somalia's Shebab Islamists said Thursday they have executed a French agent they have held since 2009, as France said the hostage was likely killed several days ago in a failed rescue attempt.

"16:30 GMT, Wednesday, 16 January, 2013. Denis Allex is executed," the group said on its Twitter feed Thursday, with the report confirmed by a senior Shebab official who said the group might release audio and video of the "execution."

The United States will on Thursday recognize the first Somali government in two decades, heralding a significant shift in ties since the deadly 1993 attack on U.S. helicopters over Mogadishu.

The beginning of a new chapter will come when U.S. Secretary of State Hillary Clinton exchanges diplomatic notes with visiting Somali President Hassan Sheikh Mohamud, a top U.S. official said Wednesday.

The African Union Mission in Somalia (AMISON) on Wednesday said it is probing the deaths of several civilians, including children, in a village to the west of the capital Mogadishu.

The force says the civilians may have been caught Tuesday in an exchange of fire with Islamist extremists, but witnesses on the ground say they were shot by AMISOM soldiers.

Somali Islamists said Wednesday they have decided to execute the French intelligence officer they have held for more than three years and who was the object Saturday of a botched rescue bid.

The al-Qaida linked Shebab in a statement said they have "reached a unanimous decision to execute the French intelligence officer, Denis Allex." Paris has said the officer was most likely killed by his captors during the failed rescue attempt.

French Prime Minister Jean-Marc Ayrault on Monday denounced the publication by Somalia's al-Qaida-linked Shebab of photographs of an alleged French commando chief killed in a botched hostage rescue operation.

"This is a particularly odious display," Ayrault told journalists in the northwestern city of Caen, after Shebab posted the photographs on its Twitter account.

Somalia's al-Qaida linked Shebab militants on Monday posted a picture on their Twitter account of an alleged French commando chief killed in a botched hostage rescue operation.

"French commander killed during botched rescue operation in Bulo-Marer," read an accompanying caption to the photo.