ADEN, Yemen, March 7 (Xinhua) -- Unknown gunmen opened fire on a police patrol in Yemen's southern port city of Aden on Thursday, leaving a policeman killed and five others injured, a government official told Xinhua.

"A group of unknown gunmen blocked the main road in KhorMaksar district of Aden and then opened fire against a police patrol, killing a policeman at the scene," the source said on condition of anonymity.

Two of the injured were in serious condition, he added.

Another source of Aden's security command told Xinhua that efforts were underway to capture the gunmen and those who blocked KhorMaksar's main road.

"Aden's security forces started tracking some sabotage elements who intended to create chaos in Aden and began to attack police forces," said the source who also asked to remain anonymous.

No group immediately claimed responsibility for the attack, but the security source blamed it on extremist groups.

Yemeni government officials, including high-ranking security commanders and intelligence officers, have been the prime targets in attacks by unknown gunmen during the past months.

Considered Yemen's temporary capital, Aden is where the Saudi-backed Yemeni government has based itself since 2015.

The impoverished Arab country has been locked into a civil war since late 2014, when Shiite Houthi rebels overran much of the country and seized all northern provinces, including the capital Sanaa.