Ethiopia has conducted air strike on the capital of the northern Tigray region for the fourth day this week, as fighting has intensified between central government and regional rebels.

Ethiopia's Government      Spokesperson Legesse Tulu said Friday’s air strike targetes a base formerly belonging to the Ethiopian military and now being used by rebel Tigrayan forces as a training site in the regional capital Mekelle, Aljazeera reported.

Getachew Reda, Spokesperson for the Tigray People’s Liberation Front (TPLF), told the Reuters the attack had hit the compound of Mekelle University. He said he has no information on casualties.

Three humanitarian sources in Ethiopia also told Reuters that the attack had hit Mekelle University.

Tigrai TV, which is controlled by the TPLF, reported that the attack hit the main campus of the university and 11 civilians were wounded.

Legesse, the government spokesperson, said the university was not hit.

The United Nations suspended all flights to Mekelle after a plane with 11 passengers had to abort landing on Friday, UN spokesman Stephane Dujarric said.

The UN flight from Addis Ababa had been cleared by federal authorities, he said, but was told “to abort landing by the Mekelle airport control tower”.

The flight safely returned to the Ethiopian capital, Dujarric said, adding that UN agencies were “carefully reviewing the circumstances” of what happened.

Legesse confirmed that authorities were aware of the inbound flight.

The development appeared to be a sharp escalation in the intimidation tactics that Ethiopian authorities have used against aid workers amid the intensifying, year-long Tigray war.

Legesse told the AP that authorities were aware the UN flight was in the area but said the UN and military flights had a “different time and direction”.

The friction between the government and humanitarian groups is occurring amid the world’s worst hunger crisis in a decade, with close to a half-million people in Tigray said to be facing famine-like conditions.

The government since June has imposed what the UN calls a “de facto humanitarian blockade” on the region of some six million people, and the AP has reported that people have begun to starve to death.

A military spokesman did not immediately respond to questions about the UN flight, which had planned to land in Mekelle, the main base of humanitarian operations in Tigray.

Independent journalist Samuel Getachew told Al Jazeera from Ethiopia’s capital Addis Ababa that “there doesn’t seem to be any willingness to compromise”.

“The Ethiopian side keeps saying they are targeting a terrorist organisation that they’ve declared earlier this year. The TPLF is saying the Ethiopian government is creating some kind of genocide. There doesn’t seem to be an end in sight,” Getachew said.

“As of Monday, media noted that three people have been killed as a result of the air strikes.”

Meanwhile, fighting escalated in Amhara, a neighbouring region where the TPLF has seized territory that the government and allied armed Amhara armed groups are trying to recover.

Residents in Dessie, a major city in Amhara, told Reuters people were fleeing, a day after a TPLF spokesperson said its forces were within artillery range of the town.

“The whole city is panicking,” a resident said, adding that people who could were leaving. He said he could hear the sound of heavy gunfire on Thursday night and into the morning, and that the bus fare to the capital Addis Ababa, about 385km (240 miles) to the south, had increased more than six-fold.

There are now more than 500,000 internally displaced people in the Amhara region, Atalel Abuhay the Director of Communications for the National Disaster Risk Management Commission told Reuters.

Seid Assefa, a local official working at a coordination centre for displaced people in Dessie, said 250 people had fled there this week from fighting in the Girana area to the north.

“We now have a total of 900 (displaced people) here and we finished our food stocks three days ago.”

Leul Mesfin, medical director of Dessie Hospital, told Reuters two girls and an adult had died this week at his facility of wounds from artillery fire in the town of Wuchale, which both the government and the TPLF have described as the scene of heavy fighting over the past week.

War erupted nearly a year ago between federal troops and the TPLF, which governed Ethiopia for three decades at the helm of a multi-ethnic coalition and now controls the northern region.

Thousands of people have been killed and more than two million have been forced to flee.

Tigray remains under a communications blackout, making it difficult to verify claims, while areas of fighting in Amhara are largely unreachable as well.