Somali refugees in Kenya must only return home voluntarily, the United Nations said Monday, after signing a deal easing fears of possible forced returns of over half a million refugees.

"Returns should be conducted in safety and dignity," said Raouf Mazou, Kenya representative of the U.N. refugee agency (UNHCR), adding that it would support organized repatriations only when "conditions are right".

Kenya charged four men Monday in connection with the Westgate mall massacre in September, an attack claimed by Somalia's Al-Qaida linked Shebab in which at least 67 people were killed.

"The accused persons carried out a terrorist attack at Westgate Shopping Mall on September 21 by supporting a terrorist group," the charge sheet read.

Kenyan warplanes have destroyed a Shebab rebel camp in southern Somalia used to train gunmen who attacked Nairobi's Westgate shopping mall in September, Kenya's defense ministry said.

Many rebels were killed in the "major aerial offensive" conducted on Thursday, said a ministry statement issued later the same day.

The International Criminal Court on Thursday postponed Kenyan President Uhuru Kenyatta's trial on charges of crimes against humanity trial by three month to February next year.

Kenyatta is accused of masterminding some of the 2007-8 post-election violence in Kenya that left over 1,000 people dead and several hundred thousand displaced.

Twelve people were killed and several others injured Wednesday when a passenger train in Kenya's capital smashed into a bus at a crossing, police said.

The train crashed into the side of the bus as it crossed the railway line during the peak hours of morning rush hour, local police commander Benjamin Nyamae said.

A United States military strike hit a vehicle carrying senior members of an al-Qaida-linked militant group in Somalia on Monday, killing at least two people including the group's top explosives expert, a militant and a government intelligence official said.

A senior U.S. military official told The Associated Press that there was a counterterrorism strike against a target in Somalia Monday but would give no further details. The official spoke on condition of anonymity because there was no authorization to discuss the strike publicly.

International Criminal Court prosecutors asked judges Monday to reverse a ruling allowing Kenya's President Uhuru Kenyatta to attend only parts of his trial, after a similar decision involving his deputy was overturned last week.

Appeals judges ruled on Friday that Kenyan Deputy President William Ruto must attend his own crimes against humanity trial, saying Ruto could only be excused under "exceptional circumstances."

Robbers have shot dead a Swiss tourist near a popular resort town in southern Kenya, police said Saturday.

The exact circumstances of his death on Friday were not immediately clear but the Swiss national was killed when criminals opened fire after robbing a shop near Diani, a beach town on the Indian Ocean.

Kenya's president has asked for his crimes against humanity trial to be postponed, citing the "national and international crisis" triggered by a deadly attack on a Nairobi shopping centre, his lawyers said Friday.

Uhuru Kenyatta is due to go on trial at the International Criminal Court (ICC) next month on charges of masterminding some of the 2007-8 post-election violence in Kenya that left over 1,000 people dead and several hundred thousand displaced.

Kenyan Vice President William Ruto must attend his crimes against humanity trial before the International Criminal Court and can only be excused under "exceptional circumstances," the ICC ruled Friday.

"The appeals chamber deems it appropriate to reverse" an earlier ruling excusing Ruto from most of his trial before the Hague court, said Judge Sang-Hyun Song.