The US has imposed travel bans on Kenyan politicians who it says continue to block government steps aimed at preventing political violence.

Sending letters to some 15 officials on Friday, the US ambassador to Kenya, Michael Ranneberger, said that Washington was reviewing its relationship with anyone in authority who was preventing political progress.

Ranneberger declined to name the individuals, but said only that Johnnie Carson, the most senior US diplomat for Africa, had sent the letters to ministers, senior government officials and members of parliament.

Al Jazeera's correspondent in Nairobi, Andrew Simmons, reports that even though little reform has taken place since the December 2007 riots that killed a thousand people, the US move has been received badly.

"There really is a question mark here over how the policy is going to work out ... so far, ministers and their spokesman have said they do not respond to 'activism diplomacy'."

Slow progress

Washington, one of Kenya's principal lenders, has persistently criticised Kenya for not taking action against perpetrators of post-election violence in 2007.

Mwai Kibaki, the president, and Raila Odinga, the prime minister, signed a power-sharing deal in February 2008 to end the violence, which was further driven by frustration over poverty and corruption.

The power-sharing deal also contained clauses on constitutional, judicial and other reforms, which have not been implemented.

"It's a growing sense of frustration, at the highest levels (in Washington), that despite the rhetoric, and commissions and talk and all that, not much has happened," Ranneberger said on Friday.

Alfred Mutua, the Kenyan government spokesman, told The Associated Press that Kenya does not "respond to activism diplomacy".