HARGEISA - Gunmen have shot dead a senior security official in Somalia's northern breakaway enclave of Somaliland, the latest in a string of attacks on security agents and government officials there, an official said.

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

"Six armed gunmen opened automatic fire on Colonel 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.

Somaliland is proud of its relative stability and 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 Shabaab rebel group fighting to topple Somalia's interim government hit the breakaway region with suicide bombs 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 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.