NAIROBI, Kenya -- The four Westgate Mall attackers -- all ethnic Somalis -- crossed into Kenya in June and settled down in Nairobi's ethnic Somali neighbourhood, where they worked out at the Andalus Gym, a Western official said Monday.

The official for the first time on Monday confirmed that all four attackers' have been identified. All four are ethnic Somali; none of the four has ever been to the U.S. or U.K., the official said.

Little has been released publicly about the attackers behind the Sept. 21 grenades-and-gunfire assault on Nairobi's upscale mall, an attack that killed at least 67 people and froze the city for four days.

Two attackers were previously identified: Hassan Abdi Dhuhulow, a 23-year-old Somalia native whose family moved to Norway in 1999. A second name was revealed in court documents as Mohammed Abdinur Said. The official on Monday declined to release the other two names, saying only that they are known. The official insisted on anonymity to discuss information not yet released publicly.

The four gunmen arrived in Kenya in June and were previously in Somalia. Officials know where the four lived in Nairobi and the gym they attended in Nairobi's Somali neighbourhood, Eastleigh. An employee of that gym -- Andalus Gym -- said in a phone call Monday he was not aware that any of the four had been to his gym.

The Somali militant group al-Shabab claimed responsibility for the attack and said it was in retaliation for Kenya's sending of troops into Somalia. The group, which is linked to al-Qaida, had threatened large-scale attacks for years, and it has said more will be carried out unless Kenya withdraws.

The mall siege was carried out by four men with AK-47 assault rifles, but the standoff turned into a four-day fiasco that saw the mall go up in flames and a section of the structure collapse. Afterward it was revealed that Kenyan army troops looted high-end merchandise inside the mall during the siege.

Remains were found in the mall's rubble that the official said are believed to be those of the attackers. The remains are being analyzed by an FBI lab. Only four attackers were seen on closed-circuit television images from the mall, despite early reports from the government of up to 15 attackers.

Kenyan officials say 67 people died in the September attack, but some two dozen people remain unaccounted for, and the official said the toll could rise as high as 94.

Despite press reports during the mall siege that the attackers had hostages and had prepositioned weapons or ammunition inside the mall, no evidence has emerged to back those claims, the official said.