Ethiopia on Tuesday claimed Sudanese forces were pushing further into a contested border region that has been the site of deadly clashes in recent weeks, warning that its "peaceful" approach to the dispute "has its limit".

The two Horn of Africa nations have long feuded over the Al Fashqa region, where Ethiopian farmers cultivate fertile land claimed by Sudan.

In early December Sudan accused Ethiopian "forces and militias" of ambushing Sudanese troops along the border, leaving four dead and more than 20 wounded.

Ethiopia, for its part, said last week that Sudan's military had "organised attacks by using heavy machine guns" and that "many civilians have been murdered and wounded".

Dina Mufti, spokesman for Ethiopia's foreign ministry, on Tuesday said Sudanese forces were still advancing into the border region, calling the move an "unacceptable and counterproductive" violation of international law.

"The current situation is the Sudanese force at the border is boosting its position and moving forward... into Ethiopia's hinterland," Dina told a press conference.

He called on Sudan to "return to the previous status quo" to give space for a demarcation process.

"Ethiopia always gives priority to peace and respects international norms. However, Ethiopia has its limit," he said.

Dina has previously accused Sudanese military officers of trying to take advantage of fighting in Ethiopia's northernmost Tigray region to press its territorial claims in Al Fashqa.

The Tigray conflict has spurred tens of thousands of Ethiopian refugees to cross into Sudan.

The two countries share a 1,600-kilometre frontier.

In 1902, a deal to draw up the border was struck between Great Britain, the colonial power in Sudan at the time, and Ethiopia, but it lacked clear demarcation lines.

The two sides held border talks in late December, and Sudan said December 31 that its army had restored control over all border territory that had been taken over by Ethiopian farmers.

The border dispute comes at a sensitive time for ties between the two countries, which are also along with Egypt trying to reach a deal over Ethiopia's massive Grand Ethiopian Renaissance Dam on the Blue Nile River.