Col. Abdi Esse Nur, regional commander of the custodian corps in Sool region, was killed outside his house in the eastern town of Las Anod late on Tuesday.

"Six armed gunmen opened automatic fire on Col. Abdi Esse Nur when he came out of his home and was entering his car. He died on the spot," Sool regional governor, Abdillahi Jama Dirie, told reporters on Tuesday night.

Somaliland is proud of its relative stability and a peaceful handover of power in July after elections that were deemed by international observers to have been largely free and fair.

But such attacks are a reminder of its vulnerability to radical militants seeking to destabilise the region.

The Al-Qaeda-linked Al-Shabab rebel group fighting to topple Somalia's interim government hit the breakaway region with a suicide bomb blast in October 2008.

In April, Somaliland deported four foreigners -- two Ethiopians, a Sudanese and an Eritrean -- it accused of involvement in a series of smaller bomb attacks on security force targets in late 2009 and early 2010.

Nur was the sixth senior security forces officer or government official to be killed in Las Anod since 2009, and the first since President Ahmed Mohamed Silanyo took office on July 27.