Ethiopia's Prime Minister Abiy Ahmed has insisted that the military operation in the Northern state of Tigray has "clear, limited and achievable objectives".

Tigrayan leader Debretsion Gebremichael has previously accused Mr Abiy's administration of plotting to invade the state. Some fear this may be the start of a civil war. The head of the UN has called for an "immediate de-escalation of fighting".

What's the latest on the fighting?

Clashes are said to be continuing in Western Tigray but details are scanty.

Ethiopia's federal army is sending more troops to Tigray, the country's northernmost state, says Gen Berhanu Jula, deputy army chief of staff, saying they were being mobilised from across the country.

That's to provide support for the Northern Command, which is based in Tigray and whose base was captured by the TPLF.

Prime Minister Abiy insisted in two tweets that this operation would be "limited" and was a last resort after trying "patiently" to resolve differences peacefully for several months.

Operations by federal defence forces underway in Northern #Ethiopia have clear, limited & achievable objectives — to restore the rule of law & the constitutional order, and to safeguard the rights of Ethiopians to lead a peaceful life wherever they are in the country.1/2

— Abiy Ahmed Ali 🇪🇹 (@AbiyAhmedAli) November 6, 2020

It comes after Mr Debretsion, head of the Tigray People's Liberation Front (TPLF), said his troops had seized "almost all" of the weaponry at the Command.

The BBC's Kalkidan Yibeltal in the capital, Addis Ababa, says the crisis is showing no signs of waning.

How serious is this?

It is difficult to know how intense the clashes have been and how many people have been killed.

That's partly because the internet and phone lines have been cut off in Tigray. However, electricity has now been restored to the region.

Schools and shops in the regional capital, Mekelle, are open, and transport services to other towns have resumed, but local residents say there is a sense of fear over what the coming days may bring.

Mr Abiy has also refrained from giving details, instead promising information would be released once operations were over.

What we do know is that there has been lots of fighting talk.

Mr Debretsion has said they are ready to fight to defend the region, which would be "a burial place for the reactionaries".

While Mr Abiy's office has accused the TPLF of "continued provocation and incitement of violence" and said "the last red line had been crossed".

Gen Berhanu also accused regional troops loyal to the Tigray People's Liberation Front (TPLF) of treason.

This tone has led observers to fear that it may be the start of a civil war, although the prime minister seemed to downplay those fears.

A statement from his office said that under the six-month state of emergency he declared in the region, a new taskforce under the control of the military chief of staff would have the power to:

• disarm any regional security force
• impose travel restrictions
• impose a curfew
• detain suspects engaged in illegal activities that endanger the constitutional order
• use proportional force to restore law and order

What's this all about?

Tension has been mounting for some time as relations between the TPLF and the federal government have deteriorated.

The TPLF used to be the dominant force in Ethiopia's ruling coalition but its power has waned since Mr Abiy became prime minister in 2018.

Last year, he dissolved the ruling coalition, made up of several ethnically based regional parties, and merged them into a single, national party, the Prosperity Party, which the TPLF refused to join.

Friday's statement from the prime minister's office also said that some members of the TPLF were "fugitives from justice" and suggested they opposed Mr Abiy's attempts to reform the way Ethiopia was run.

Relations took a significant turn for the worse after the TPLF held a regional election in September.

The Tigrayan authorities went ahead with the vote in defiance of a nationwide postponement that was put in place following the outbreak of coronavirus.

The federal government described that election for the Tigray parliament as "illegal".

The vote raised concerns that the TPLF was laying the groundwork for the creation of a breakaway state, with a parliament and government taking office without the blessing of the federal government.

The TPLF said that it was committed to keeping the region within Ethiopia, but insisted it would defend "self-rule" and oppose what it called Mr Abiy's attempt build a strong "unitary" state.

This week, Mr Abiy accused the TPLF of attacking the military base and sent in the Ethiopian military.

The federal government has also declared a six-month state of emergency in the state of Tigray, and airspace in the region has been closed.

What are diplomats saying?

The UN Secretary General António Guterres said he was "deeply alarmed" and called for an "immediate de-escalation of fighting".

I’m deeply alarmed over the situation in the Tigray region of Ethiopia.

The stability of Ethiopia is important for the entire Horn of Africa region.

I call for an immediate de-escalation of tensions and a peaceful resolution to the dispute.https://t.co/nWtI2JtGlu

— António Guterres (@antonioguterres) November 5, 2020

Previously, on Wednesday, amid the drama of the US election, US Secretary of State Mike Pompeo also called for an end to any fighting.

"We are saddened by the tragic loss of life and urge immediate action to restore the peace and de-escalate tensions... the protection of civilian safety and security is essential," he said in a statement.

The African Union, whose headquarters are in the Ethiopian capital, Addis Ababa, is pushing for talks but the government is not willing to negotiate, sources told the Reuters news agency.