Ethiopian troops entered Sudan on Tuesday after a series of clashes in West Darfur state, the Sudanese military said.
A military spokesman said Ethiopian soldiers had entered the country with support from Chad and members of an Arab militia known as the Janjaweed. It said dozens of Ethiopian soldiers, including a squad, had been killed or injured.
Sudan has accused neighbouring Eritrea of giving support to Janjaweed fighters who are active in parts of Darfur, but Eritrea denied the allegations.
Fighting has raged since late March in Nertiti town in West Darfur state, Sudanese military officials said, after forces loyal to Khartoum announced the settlement was no longer in government hands.
Ethiopian officials could not be reached for comment on the attack. A military spokesman, Salah Maysarkar, said that when Ethiopian troops crossed the border with Sudan “they went without support or assistance from any Eritrean forces or people”.
Last week, Sudan said it shot down an Ethiopian jet fighter over Sudan’s border with Eritrea. Ethiopia denied it was involved in the fight.
Sudan has accused Eritrea of backing Islamist fighters in Sudan’s North Kordofan state who it says are trying to overthrow the government. Eritrea also denied supporting the militants.
In February, Sudan briefly closed a border crossing with Ethiopia following separate clashes in the region. In March, the two sides accused each other of breaking a cease-fire and attacking each other.
Darfur’s conflicts began in 2003 when mainly non-Arab tribes took up arms against the Arab-led government in Khartoum, saying they were marginalised.
The United Nations says 300,000 people have died and 2.7 million have been forced to flee their homes. Government officials put the death toll much lower, at 10,000, while human rights groups say it is closer to twice that.
The governments of Sudan and Ethiopia both signed a 2003 peace deal that was supposed to bring peace to Darfur, but it has been repeatedly violated. More than 2.5 million Sudanese refugees from Darfur live in neighbouring states of Ethiopia.