NAIROBI - A grenade attack on a club in the centre of Nairobi early on Monday wounded 14 people who needed hospital treatment, Kenyan media reported.

There was no official confirmation from police about the blast, which came a week after Kenya launched a cross-border operation against al-Qaida-linked al Shabaab militants in southern Somalia after a wave of kidnappings of foreigners on Kenyan soil. ?

Al Shabaab had threatened major reprisals if Kenyan troops did not withdraw, prompting the US embassy in Kenya to warn of an 'imminent threat' of a terrorist attack in the East African country.

Al Shabaab have denied responsibility for the kidnappings, saying Kenya was using them as a pretext for its military campaign.

Kenya has in the past initiated brief cross-border incursions, but the latest operation is on a much larger scale raising fears Nairobi could be dragged into the anarchic Horn of Africa's two-decade-civil war.

The Islamist militants have proven capable of launching large scale suicide attacks within Somalia and outside.

Earlier this month, a suicide truck bombing claimed by the militants killed more than 70 people when it exploded outside a compound housing government ministries in Somalia's capital Mogadishu.

The militants have also claimed responsibility for a bomb attack in the Ugandan capital, Kampala, which killed 79 people last year. That strike, the militants' first on foreign soil, was in revenge for Uganda's contribution to the 9,000-strong AU peacekeeping force.