A fresh humanitarian crisis has broken out in Africa with fighting escalating between Ethiopian government forces and the local governing party in the northern Tigray region.

A week of violence has left hundreds dead and thousands displaced with 11,000 Ethiopians reported to have crossed into neighbouring Sudan, where local officials say they are overwhelmed.

Nine million people living in the Tigray region are said by the UN to now be at “high risk” and there are fears that the conflict could spread to other areas of Ethiopia and draw in other Horn of Africa nations.

The conflict has put at risk Ethiopia’s transition to multi-party democracy as well as threatening a humanitarian disaster.

The conflict flared when Prime Minister Abiy Ahmed ordered a military intervention last week against the region’s powerful ruling party, the Tigray People’s Liberation Front (TPLF), after reports of attacks on government military bases.

Aid operations in Tigray, which hosts around 200,000 internally displaced people and refugees from neighbouring Eritrea, have been severely curtailed, the UN’s aid coordination body, OCHA, says.

Tensions between the TPLF and the federal government have been escalating since September, when Addis Ababa indefinitely postponed regional and national elections because of the COVID-19 pandemic. TPLF officials opposed the decision and organised their own elections.

An ethnic Tigrayan party, the TPLF was the dominant force in Ethiopian politics until Abiy took office in 2018. Its members have since lost positions within the central government, and several officials have been arrested for corruption and human rights abuses.

On Monday, Abiy said the Tigray operations would “wrap up soon”. But analysts fear an all-out civil war that could trigger broader unrest within Ethiopia, where different regions are agitating for more self-rule or threatening to break away altogether.

Neighbouring states could also be drawn into the conflict, particularly Sudan, which is also experiencing a trouble political transition, and Eritrea, which sits across the border from Tigray and has a long-standing enmity with the TPLF.

A report from OCHA has warned that the conflict could cause “massive displacements” in Tigray, a region where more than two million people are already in need of humanitarian assistance.

It stated that restrictions on air and road travel were significantly affecting humanitarian operations, while the UN’s refugee agency, UNHCR, said it was struggling to provide support to refugees in camps in the region.

Efforts to combat an invasion of locusts have also been scaled back in Tigray – which is among the country’s regions most affected by the pest – just as new swarms are expected to arrive in the coming weeks.

Just cix percent of Ethiopia’s more than 100 million population live in Tigray, but local officials have dominated the country politically since the TPLF led a guerrilla struggle that defeated the country’s Marxist junta, known as the Derg, in 1991.

In power, the TPLF introduced a new constitution that saw Ethiopia divided into nine ethnically based regions – each with their own security forces, parliaments, and the right to secede.

The party was the driving force within the Ethiopian People’s Revolutionary Democratic Front (EPRDF), a coalition of ethnic parties that was controlled by the TPLF and ruled with an iron fist for almost 30 years.

The removal of Tigrayan officials after Abiy – an ethnic Oromo – came to power on the back of mass protests against the EPRDF, fuelled by a sense of ethnic discrimination among party members.

Then, last November, Abiy dissolved the EPRDF, creating a “pan-Ethiopian” national party, known as the Prosperity Party, which opposition groups considered an attempt to centralise state power and deconstruct the federal system. The TPLF refused to join.

Since the TPLF won regional elections in September, both sides have described each other as illegitimate, while the finance ministry in Addis Ababa has frozen money to Mekelle, Tigray’s capital – a move TPLF leaders have said was a “declaration of war”.

Tigrayan leaders have complained of being unfairly targeted in corruption prosecutions, removed from top positions and blamed for the country’s problems.

Both sides of the conflict are heavily armed. The national army has redeployed troops to Tigray from across Ethiopia amid concerns about the loyalty of the Northern Command, which constitutes a large proportion of the country’s overall number of troops.

Tigray’s regional forces and local militias are believed to number as many as 250,000 – many of them experienced veterans from past conflicts against the Derg and Eritrea.

Observers say a sustained conflict could spread to other regions of Ethiopia such as Amhara, which has a longstanding claim to territories in western Tigray, and whose regional forces and militias are supporting the federal government’s offensive.

If the Ethiopian government and army is weakened by the TPLF, opposition groups in other regions could also be emboldened. The risk is particularly high in Abiy’s home region of Oromia, where separatist rebels are fighting for independence.

A full-scale civil war could draw in Eritrea, whose president, Isaias Afwerki, has grown increasingly close to Addis Ababa since the two sides agreed to an historic rapprochement in 2018 that won Abiy the Nobel Peace Prize.

Meanwhile, refugees fleeing the conflict have claimed both sides are committing atrocities against civilians, and described hospitals struggling to cope with casualties.

Amnesty International has reported that scores, possibly hundreds, of civilians were massacred with knives and machetes in a town south of Humera last week.