The negotiations come more than six months after a first round of discussions between the Oromo Liberation Army (OLA) and Ethiopia's government ended without an agreement. The conflict in recent years has killed hundreds of people and displaced tens of thousands in Ethiopia's most populous region.
"We remain committed to finding a peaceful political settlement," the OLA said in its statement.
The OLA said it had delayed announcing the negotiations to make sure its team could get safely from what it called the frontlines in Oromiya to the venue.
An official close to the mediators, who spoke on condition of anonymity, said the talks started last week in Tanzania's commercial capital, Dar es Salaam, and is being facilitated by the regional Africa group IGAD.
Ethiopia's government did not immediately respond to a request for comment.
The OLA is an outlawed splinter group of the Oromo Liberation Front, a formerly banned opposition party that returned from exile after Prime Minister Abiy Ahmed - himself an Oromo - took office in 2018.
FILE —In this September 15, 2018 photo, a man holds an Oromo Liberation Front (OLF) flag as hundreds of thousands of Ethiopians gathered to welcome returning leaders of the once-banned group in the capital Addis Ababa, Ethiopia.
Oromiya, which surrounds Addis Ababa, the capital, is home to Ethiopia's largest ethnic Oromo group and more than a third of the country's 110 million people.
The talks come as conflict rages on another faultline in Ethiopia, with fighting between the army and the Fano militia group in the mediaeval holy city of Lalibela last week, residents told Reuters. The government said the area was peaceful.
While Fano has no formal command structure, the part-time militia in northern Amhara region has been battling the army since late July, emerging as the biggest security challenge to Abiy since a war ended in the northern Tigray region a year ago.