Image copyright (C) British Broadcasting Corporation Image caption The attack comes as Kenya celebrates 50 years of independence from Britain

A grenade has been thrown at British tourists in Mombasa, Kenya, but failed to explode, police have said.

The head of Kenya's anti-terror police unit said officers were in pursuit of the attacker. Police say a man fled after throwing the grenade.

The two British tourists were in a vehicle travelling in the Likoni district, local media said.

The Foreign Office said it was urgently looking into the reports.

Mombasa police chief Robert Kitur said the grenade had been detonated safely by experts.

The tourists were travelling from the Indian Ocean coastal resort of Diani to a wildlife safari at Kenya's world famous Maasai Mara national park.

According to Kenya's Standard newspaper the driver went to a police station to report the incident.

The British High Commission in Kenya said they had "heard the reports and are investigating", but gave no further details.

The attack comes as Kenya celebrates its 50 years of independence from former colonial rulers Britain.