Police in the Kenyan capital, Nairobi, say a grenade attack at a nightclub has wounded at least 13 people.

Authorities say someone threw a grenade into the club early Monday, days after the U.S. embassy in Kenya warned of an imminent terrorist attack in the country.

The U.S. did not specify who might carry out such an attack, but said the likely targets would include places where foreigners congregate, such as shopping malls and nightclubs.

No one has claimed responsibility for the attack, and police said Monday they are investigating if it is linked to the threat.

The blast comes a week after Kenya carried out a cross-border operation against al-Qaida-linked al-Shabaab militants in southern Somalia, after a wave of kidnappings of foreigners on Kenyan soil.