* Mall attack the worst in Kenya since 1998 bombing
* Somali Islamist militant group has threatened more attacks
* Alleged attacker seen smiling on CCTV footage
By James Macharia
NAIROBI, Oct 5 (Reuters) - Kenya's government said a Sudanese man trained by al Qaeda was among the leaders of a raid on a Nairobi shopping mall in which at least 67 people were killed, the worst attack in the country in 15 years.
Al Qaeda-linked group al Shabaab has claimed responsibility for the assault two weeks ago on the Westgate centre, saying it was an act of revenge for Kenya's military campaign in Somalia, but the identities of the gunmen have remained unclear.
A Kenyan military spokesman on Saturday named four of the attackers, saying they also included a Kenyan Arab and a Somali.
Closed-circuit television footage from the Westgate mall was broadcast on Kenyan television channels that appeared to show four men with guns and backpacks apparently carrying ammunition walking around the mall's supermarket and a storage room.
Major Emmanuel Chirchir, the spokesman for the Kenya Defence Forces (KDF), named the four as Abu Baara al-Sudani, Omar Nabhan, Khattab al-Kene and Umayr.
"I confirm these were the terrorists. They all died in the raid," Chirchir told Reuters, citing the findings of the KDF and national intelligence bodies.
He said Al-Sudani, which means "The Sudanese", was the leader of the group shown in the CCTV footage and was trained by al Qaeda.
"He is an experienced fighter and sharpshooter," he said.
Nabhan, a Kenyan of Arab origin, was born in the coastal city of Mombasa and travelled to Somalia with his uncle at the age of 16, said Chirchir.
Al-Kene was thought to be from the Somali capital Mogadishu, and was linked to country's al Shabaab militants, he said.
Umayr's full name, nationality and background were "not yet identified", Chirchir added.
Kenya has said as many as 15 militants took part in the raid and the authorities were holding nine of them. The government said five of the attackers were killed, but survivors say some may have escaped.
Al Shabaab militants said on Saturday that Western forces had raided a coastal town under cover of darkness and killed one of their fighters. It was not clear whether the assault was related to the attack on the Kenyan mall.
Chirchir said he was trying to get details of the attack in Barawe, about 180 km (110 miles) south of Mogadishu.
Matt Bryden, the former head of the United Nations Monitoring Group on Somalia and Eritrea, said al-Kene and Umayr were known members of al Hijra, the Kenyan arm of al-Shabab.
Bryden said al Hijra is not simply an Al-Shabaab offshoot. Its roots pre-date al Shabaab, stretching back to early al Qaeda networks in East Africa.
"Nabhan obviously suggests and association with the Al-Qaeda East Africa cell leader killed in Somalia in 2009, but it remains to be seen if this is a coincidence or something more," said Bryden through email.
Nabhan was killed by helicopter-borne U.S. special forces in southern Somalia, suspected of building the bomb that killed 15 people at an Israeli-owned hotel on the Kenyan coast in 2002.
The Westgate attack, Kenya's worst since al Qaeda bombed the U.S. embassy in 1998 and killed more than 200 people, has shocked Kenyans and confirmed fears in the region and the West that Somalia remains a training ground for militant Islam.
Al Shabaab, who want to impose their strict version of sharia, or Islamic law, across Somalia, were driven out of Mogadishu in late 2011. They are now struggling to hold on to territory elsewhere in the face of attacks by Kenyan, Ethiopian and African Union forces.
The CCTV footage obtained by the local TV stations showed the attackers walking casually through a supermarket, holding machineguns and speaking on mobile phones.
The man Chirchir identified as Al-Sudani is seen walking into a storage room. He then beckons to his colleagues to join him and they walk into the frame one by one.
He walks about with what appears to be a bandaged leg, apparently from a bleeding wound, but is not seen limping.
A second piece of footage shows him rifling through a cash register at the Nakumatt chain store, where many people were killed, according to witness accounts.
In one image he appears to be smiling.
"The investigations are progressing well, and we are optimistic some people will be prosecuted soon," Kenya's Inspector General of police David Kimaiyo told Reuters. He declined to give more details about the case.