Ethiopia’s prime minister has warned that a three-day deadline for rebel regional forces to surrender has expired, paving the way for a final push on Mekelle, the capital of the northern region of Tigray.

Tigrayan forces fired rockets into neighbouring Eritrea at the weekend, escalating a conflict in which hundreds of people have been killed on both sides and threatens to destabilise other parts of Ethiopia and the Horn of Africa. More than 25,000 refugees have fled to Sudan.

Abiy Ahmed’s warning came after government troops carried out “precision-led and surgical air operations” outside Mekelle, a government emergency taskforce said, and ground forces moved forward.

“The three-day ultimatum given to Tigray Special Forces and the militia to surrender to the national defence … have ended today,” Abiy said in a statement posted on Facebook.

“Following the expiration of this deadline, the final critical act of law enforcement will be done in the coming days.“

There was no immediate comment from Tigray’s leaders. With communications mostly down and media barred, it is not possible to independently verify assertions made by any side.

Tigrayan forces could dig in as the military advanced into the more mountainous terrain towards Mekelle, said Matt Bryden, the founder of Sahan, a Nairobi-based regional thinktank.

“I would guess as the Ethiopian army enter the highlands, heavier fighting is likely to start.”

The government did not say when the latest airstrikes outside Mekelle took place but diplomats and military sources said they came mid-morning on Monday.

The strikes were based on “information received of specific critical TPLF (Tigray’s ruling party) targets”, the taskforce said, adding that no civilian targets were attacked.

Tigrayan leaders had accused the government of targeting a sugar factory and a dam.

A convoy of four buses and several cars, carrying about 400 foreigners from Mekelle, was expected to arrive in the capital on Wednesday, five diplomatic sources said.

Another convoy carrying about 200 passengers, mainly workers for international organisations, reached the capital late on Monday, the sources said.

The United Nations, the African Union and various countries are pressing for talks, but Abiy has resisted, saying the government would negotiate only when it restored the rule of law in Tigray.

On Monday, Abiy sent his foreign minister to Uganda and Kenya to explain what the government describes as an internal conflict to leaders of those countries. Ethiopian officials said the visits did not mean negotiations had started.

Ethiopia, Africa’s second most populous country, has long been a diplomatic heavyweight and western ally in a region roiled by conflict and militancy.