Somali Prime Minister Abdi Farah Shirdon said Tuesday that those behind Nairobi's deadly mall siege which has been claimed by Somalia's Shebab militants, must be brought to justice.

"Those responsible must be held accountable," the premier said during a U.N. human rights meeting in Geneva. "This tragedy has brought our countries closer."

Kenya's president announced Tuesday that a siege of a Nairobi shopping mall was over, but said losses from the attack by Islamist gunmen were "immense" and at least 67 people had died.

"We have ashamed and defeated our attackers, that part of our task is completed," President Uhuru Kenyatta said in a televised address to the nation.

The African Union and United Nations vowed Tuesday to step up the fight against al-Qaida-linked Shebab militants in Somalia following the deadly siege in Kenya now in its fourth day.

"Our resolve is to fight now more than ever before," the deputy head of the AU's executive branch, Erastus Mwencha, told Agence France Presse.

A senior U.S. lawmaker on Sunday called for careful surveillance of the American Somali community in the wake of a deadly militant attack on a Kenyan shopping mall.

Peter King, chairman of the House of Representatives committee on counterterrorism and intelligence, said up to 20 Americans are currently members of Somalia's Shebab militia.

The EU hosts a "milestone" international conference on Somalia on Monday aimed at underpinning economic and political recovery after two decades of bloody civil war.

Some 50 high-level delegations from Africa, Europe, the Gulf and elsewhere are expected for the "New Deal in Somalia" event, gathering President Hassan Sheikh Mohamud, other Somali leaders, world aid groups and global finance institutions.

A U.S. Islamist fighting in Somalia was killed Thursday in a shootout with al-Qaida linked Shebab militants, former comrades he had fallen out with, witnesses said.

Alabama-born Omar Hammami -- better known as Al-Amriki or "the American" -- was one of the most prominent foreigners fighting in Somalia, and the U.S. State Department had offered a $5 million (3.8 million euro) bounty for his capture.

Somalia's al-Qaida-linked Shebab insurgents on Wednesday celebrated the anniversary of the September 11, 2001 attacks with a Twitter eulogy for the "courageous" hijackers.

In a series of posts on Twitter, the Islamists vowed "the mujahideen will continue with their jihad against the West until the world is ruled by one sovereign state, an Islamic state".

Somali-born activist and former supermodel Waris Dirie on Wednesday opens a center in Germany to treat victims of female genital mutilation, which she was subjected to as a child.

About 8,000 young girls are circumcised every day in Africa and the Middle East, and the Desert Flower Medical Center, located in a Berlin hospital, will offer reconstructive surgery and psychological help to those among the 50,000 girls and women in Germany who need it.

The European Commission said Monday it is providing another 124 million euros for the African Union security mission in Somalia as the country recovers from years of bloody conflict.

The Commission, the EU's executive arm, said the new funding for the African Union Mission in Somalia (AMISOM) will "be critical" to its U.N. mandate "to carry out active peace support operations across Somalia."

At least 18 people were killed in the Somali capital Mogadishu Saturday when two blasts ripped through a busy parking lot next to a restaurant, police said, in attacks quickly claimed by Shebab Islamists.

"There were two heavy explosions at a parking lot near the National Theatre," police officer Mohamed Adan told Agence France Presse.