Opposition leaders in the separatist Somali region of Somaliland on Sunday slammed as unlawful a decision to extend the term of the president by two years ahead of its expiry next month.

A powerful council of elders on Saturday voted to extend President Muse Bihi Abdi's term of office to 2024, saying the move is to end a protracted political conflict.

But opposition leaders in the self-declared republic rejected the move and denounced a lack of consultation ahead of the announcement.

"We were embarrassed with the decision. The democratic electoral system was dumped and exposed to darkness yesterday and the confidence of the public and their desire suppressed," Wadani party leader Abdirahman Mohamed Abdullahi told reporters in the capital Hargeisa.

"The president has intentionally resorted to illegitimacy, breach of the constitution and recklessness," he added, vowing not accept his term extension.

A presidential election had been due to take place on November 13, a month before Abdi's original term expired.

However, the region's electoral body last week pushed it back by nine months citing technical and financial constraints.

After Saturday's announcement of the two-year extension it is unclear when that vote will be held.

The rejection of the proposed term extension fuels worries about a possible return to deadly violence.

The run-up to the scheduled poll was marred when several people were killed and dozens wounded in early August after police fired on anti-government demonstrators in several towns, according to opposition party members and witnesses.

Decisions of the elders' council -- the Guurti -- often go unchallenged.

Composed of unelected traditional Somaliland elders, the Guurti is the most powerful body in the separatist region.

It has the final say in resolving political issues, including disputes in parliament.

Another opposition leader Feysal Ali Warabe, head of the Justice and Welfare party (UCID), said they will cease to recognise the legitimacy of President Abdi from November 13.

"We will not recognise him as president and Muse Bihi will take responsibility for any violence or instability that follows," he said.

A former British protectorate, Somaliland declared independence from Somalia in 1991 but the move has not been recognised by the international community, leaving the Horn of Africa region of about four million people poor and isolated.

Somaliland has however remained relatively stable while Somalia has been wracked by decades of civil war, political violence and an Islamist insurgency.