Kenya has asked the UN security council to delay the International Criminal Court (ICC) trials of President Uhuru Kenyatta and his deputy William Ruto because of the terrorist threat in east Africa.

They face crimes against humanity charges for their alleged roles in violence following the 2007 general election which killed more than 1,000 people.

The pair deny the charges and have ramped up their bid to have the trials put back since last month's attack on the Westgate shopping centre in Nairobi.

Kenya's UN ambassador Macharia Kamau asked the council to take into account threats to peace or an act of aggression "likely to transpire in light of the prevailing and continuing terrorist threat existing in the Horn of and eastern Africa" in a letter obtained by the Associated Press on Wednesday.

Mr Kamau said a delay would enable Kenya to consult the ICC on "how best to respond to the threat to international peace and security in the context of the Kenya situation."

His request was backed by the African Union, which sent an accompanying letter asking the security council to "positively" consider a delay.

It rejected a bid to delay the trial in May and several diplomats said it was likely to do the same again, despite Kenya's hopes that the deadly Westgate attack will cause a shift in opinion.

Mr Kenyatta pledged to co-operate with the ICC during his 2013 election campaign but has since tried to weasel his way out of it.