Ethiopia's government denied on Monday that northern forces whom its troops have fought for a month would be able to mount a guerrilla insurgency, while diplomats said a United Nations team was shot at while trying to visit a refugee camp.

Federal troops have seized the regional capital Mekelle from the former local ruling party, the Tigray People's Liberation Front (TPLF), and declared an end to their month-long offensive.

But TPLF leaders say they are fighting back on various fronts around Mekelle. Ethiopia experts fear a drawn-out insurgency with a destabilising impact around east Africa.

"The criminal clique pushed a patently false narrative that its fighters and supporters are battle-hardened and well-armed, posing the risk of protracted insurgency in the rugged mountains of Tigray," Prime Minister Abiy Ahmed said in a statement.

"It also claimed that it has managed to undertake strategic retreat with all its capability and regional government apparatus intact. The reality is the criminal clique is thoroughly defeated and in disarray, with insignificant capability to mount a protracted insurgency."

There was no immediate TPLF response.

With communications largely down and access for humanitarian workers and media restricted, Reuters has not been able to verify claims from all sides on the state of fighting.

A UN security team seeking to access Shimelba refugee camp, one of four for Eritrean refugees in Tigray, was blocked and fired at on Sunday, two diplomatic sources said.

The sources declined to give more details, saying the full circumstances were unclear. There was no immediate comment from the government or the TPLF.

In New York, UN spokesman Stephane Dujarric told reporters he was aware of the reports about a team being shot at, but "for a variety of reasons I'd rather not comment at this point".

Aid Needed Fast

UN Secretary-General Antonio Guterres said he was very concerned about the situation in Tigray and had discussed it with Abiy and other regional leaders on Monday. He called for the rapid restoration of the rule of law, full respect for human rights and a guarantee of unfettered humanitarian access.

The conflict, which came after Abiy had pushed back against the TPLF's past dominance of federal government and accused them of abuses, is thought to have killed thousands of people.

It has also sent nearly 50,000 refugees fleeing to Sudan, seen TPLF rockets fired into Eritrea, stirred ethnic divisions, and led to the disarming of Tigrayans in Ethiopia's peacekeeping contingency combating al Qaeda-linked militants in Somalia.

The United Nations and aid agencies are pressing for safe access to Tigray, which is home to more than 5 million people and where 600,000 relied on food aid even before the war.

The government says that with peace restored, its priorities are the welfare of Tigrayans and return of refugees. But some residents, diplomats and the TPLF say clashes persist, with protests and looting also reported in Mekelle on Friday.

The Ethiopian government issued arrest warrants for 10 senior police officers in Addis Ababa on Monday, saying they had committed treason and rights abuses by accepting unspecified missions for the TPLF, according to state-controlled media.

The TPLF dominated government for nearly three decades, until Abiy took office in 2018 and began democratic reforms.

The party accuses him of seeking to centralise power at the expense of Ethiopia's 10 regions and says Tigrayan officials were unfairly targeted in a crackdown on corruption and rights abuses. The government denies that and accuses TPLF leaders of treason for attacking federal forces in early November.

Senior TPLF leaders including its head, Debretsion Gebremichael, are hiding in mountains where troops were closing in on them, the military has said. State-affiliated broadcaster Fana said the army captured more than 40 vehicles after TPLF leaders fled on foot.