Twenty-one inmates escaped after a brazen attack on a prison early Tuesday in west Kazakhstan's Mangystau province and 13 were still on the run, justice authorities said.

The prison break, backed by armed groups, occurred at about 4:30 a.m. local time (2230 GMT Monday) in Aktau, the provincial capital. A guard was shot and injured in the incident, local media said.

A spokesman of the Kazakh Justice Ministry said troops were fanning out to hunt down the jailbreakers. A number of them were shot by the troops, but no details were revealed.