Unknown gunmen stormed a police station on Thursday, killing two policemen and injuring three others in the northern Kenyan town of Mandera.

Regional police commander Charlton Mureithi confirmed the incident, which took place at 3 am on Thursday and left more than 10 vehicles extensively damaged after being burned.

Witnesses said the gunmen launched a rocket-propelled grenade at the local administrator’s office before burning it, and spent a lot of time in the police station before escaping.

"No arrests have been made, but we hope to catch up with them. They caused huge destruction," Mureithi said.

He said authorities have launched investigations to establish the motives of the attackers, who also threw an explosive device at a building at the police station before they escaped.

The attack came hours after a civilian was killed and four others injured in the northeastern town of Wajir on Wednesday evening after unknown gunmen hurled two grenades into a crowd. Only one of the grenades exploded.

The two attacks occurred after al-Qaida allied al-Shabaab militants stormed a shopping mall in Nairobi on Saturday and killed more than 61 civilians and six security officers.

An investigation is underway to establish the identities of the terrorists behind the Westgate attack. It is not clear whether the two attacks in Mandera and Wajir were related to the bloodbath in Nairobi.

US, British and Israeli agencies are helping Kenya investigate the attack claimed by the Somali Islamist militants, officials said on Wednesday.

President Uhuru Kenyatta said on Tuesday that troops had defeated the al-Shabaab group after a four-day siege at the shopping center popular with prosperous Kenyans and foreigners. He declared three days of mourning.

The attack has highlighted the reach of al-Shabaab and the capabilities of its crack unit that claimed responsibility for the bloodshed in the Westgate mall, confirming international fears that Somalia would remain a recruiting and training ground for militants as long as it remained in turmoil.

The militants stormed the mall, known for its Western shops, in a hail of gunfire and grenades at lunchtime on Saturday.

Xinhua—Reuters