The African Union (AU) called for calm in Somaliland on Thursday after lawmakers scuffled in parliament and one drew a pistol in an angry dispute over the postponement of an election planned this month.

Somaliland has enjoyed relative peace compared with the rest of Somalia since the Horn of Africa nation plunged into anarchy in 1991. But persistent delays to presidential elections have worried rights groups and angered opposition politicians.

Nicolas Bwakira, the special envoy of the AU Commission chairman, expressed his concern about the rising tensions after a ballot due on September 27 was postponed.

"The AU special representative calls upon all parties to remain calm and avoid pronouncements and actions that may lead to further deterioration of the situation and further urges all parties to desist from any form of violence," an AU statement said.

"He regrets that if the current situation slips into a state of lawlessness, there will be worsening humanitarian conditions similar to that in the rest of the country."

Violence has killed more than 18,000 Somalis since the start of 2007 and driven another 1.5 million from their homes, triggering one of the world's worst humanitarian emergencies.

Politicians traded blows in Somaliland's parliament on Tuesday after officials agreed to debate a motion to impeach the president of the breakaway enclave over the election delays.

One lawmaker began waving a pistol before police burst in and ordered the rowdy politicians out of the chamber.

A poll set for July was put back to September 27. But the electoral commission postponed the election again this week due to worries about whether a vote could be held in the current political climate amid disputes over new electoral lists.

The motion to impeach President Dahir Riyale Kahin was presented on Saturday and the legal advisor to the lower house told lawmakers on Tuesday that the move was legal -- prompting an angry response from ruling party politicians.

Somaliland is governed by an opposition-led house of representatives elected by the people and an upper house made up of clan elders. The House of Elders has twice extended President Kahin's mandate and it is now due to expire on October 29.