Ethiopia signed a peace deal on Sunday with Ogaden National Liberation Front (ONLF) rebels from its eastern Somali Region, whom it had previously outlawed as a "terrorist group," officials said.

The ONLF launched its bid for secession of the predominantly ethnic Somali region, also known as Ogaden, in eastern Ethiopia in 1984.

In 2007, Ethiopian forces launched a large-scale offensive against the group after the rebels killed 74 people in an attack on a Chinese-run oil facility.

Earlier this year, parliament removed the ONLF from a list of banned movements along with two other rebel groups, the Oromo Liberation Front (OLF) and the Patriots/Ginbot 7 (PG7). The move was part of a reform drive being led by Prime Minister Abiy Ahmed, who has extended an olive branch to opponents. The ONLF declared a ceasefire in August.

Following a call by Ahmed, all but ONLF officially returned to the country to pursue a peaceful political contest.

An Ethiopian government delegation including Foreign Minister Workneh Gebeyehu met with the ONLF leaders in Asmara, Eritrea, a former breakaway region of Ethiopia that also witnessed reconciliation with Addis Ababa after Ahmed became prime minister on April 2, 2018.

The agreement, seen by Reuters, stipulates that both sides would end hostilities and that the ONLF would "pursue its political obligations through peaceful means".

The two sides will now form a joint committee to discuss the root causes of the conflict, the agreement said.

The Ogaden region contains four trillion cubic feet of gas and oil deposits, the government says. China's POLY-GCL Petroleum has been developing two gas fields there since 2013.

Abiy, who took office in April, is presiding over a push to shake the Horn of Africa nation of 100 million people from decades of security-obsessed rule.

He has acknowledged and condemned widespread abuses by the security forces, likening the situation to state terrorism, and he has worked to forge peace with Eritrea, with which Addis Ababa has been locked in a military standoff since a 1998-2000 border war in which 80,000 people are thought to have died.