The World Cross Country Championships due to take place in Kenya this month could be the target of a possible terrorist attack, the US has warned.
Participants from 69 countries are due to take place in the event
The US Embassy in Kenya said extremists might launch an unspecified attack during the marathon race on 24 March.
But governing body Athletics Kenya said such alerts were commonplace and athletes need not be concerned.
Some 250 people were killed in Nairobi in 1998 during simultaneous attacks on US embassies in Kenya and Tanzania.
The 1998 attacks and a subsequent attack on an Israeli-owned hotel near Mombasa four years later have been blamed on al-Qaeda.
The International Association of Athletics Federations (IAAF) says participants from 69 countries are expected at the annual championships taking place in the port city of Mombasa.
Jennifer Barnes, a spokeswoman at the US embassy in Nairobi, said they had no further details on the possible attack.
The statement circulated by the US on Tuesday warned American citizens against frequenting prominent places in Mombasa and elsewhere and asked them to be vigilant.
"The US embassy is also aware of public statements by leaders of Kenya's coastal Muslim community threatening to disrupt the world cross country championships through unspecified means," it said.
The chairman of Athletics Kenya, Isaiah Kiplagat, who is leading the local committee planning the cross country event, has dismissed the alert.
"We have always had such threats. During the Olympics in Athens there were such threats but there was no single incident," he said.
"Kenya has put in place adequate security and the athletes coming should not be scared."
Officials say Internal Security Minister John Michuki will be meeting Muslim leaders in Mombasa next week ahead of the world championships.
The Council of Imams and Preachers of Kenya (CIPK) warned that they would disrupt the event in response to alleged harassment of Muslims by the Kenyan police.
"We are going to have a very big demonstration during that time to show the world that Muslims are marginalised in Kenya," said Sheikh Mohammed Dor, the council's secretary-general.