Eritrea slammed the United States on Saturday for slapping new sanctions on the country over the deadly conflict in neighbouring Ethiopia, calling the move "illicit and immoral".

The US measures announced on Friday came in response to Eritrea's decision to send troops into Ethiopia's Tigray region to back Prime Minister Abiy Ahmed in the war against the Tigray People's Liberation Front (TPLF) rebel group.

Eritrean and Ethiopian forces have been accused of carrying out mass rapes and massacres in Tigray and Washington has repeatedly urged Asmara to pull out of Ethiopia.

On Saturday Eritrea said the sanctions reflected a "misguided and hostile policy" by the US, and were based on false allegations.

"This unilateral sanction, that shifts blame to and scapegoats Eritrea on the basis of spurious allegations, is in contravention of international law, and constitutes a flagrant breach of... sovereignty," the ministry of information said in a statement.

"That the primary aim of the illicit and immoral sanctions is to inculcate suffering and starvation on the population so as to induce political unrest and instability is patently clear."

The sanctions target the Eritrean Defense Force and President Isaias Afwerki's political party, the People's Front for Democracy and Justice, as well as other players in the closed authoritarian state.

The US has warned that Ethiopia risks "implosion" without a negotiated settlement, with Secretary of State Antony Blinken threatening to impose sanctions against Abiy's government and the rebels unless they move forward on talks.

"We are not imposing sanctions at this time on elements aligned with the government of Ethiopia and TPLF to allow time and space to see if these talks can make progress," Blinken said, ahead of a three-nation trip to Africa next week.

But Cameron Hudson, a former US official now at the Atlantic Council, said the sanctions had missed the mark.

"Prime Minister Abiy remains in the driver's seat of this conflict and choosing to once again avoid sanctioning Ethiopian entities reflects a belief from Washington that Abiy can be engaged and his approach to this conflict changed," he said.

"There is nothing particularly in evidence to support that assumption, however."

- Rights abuses -

As fighting has dragged on, the humanitarian toll has spiked, with reports of massacres and mass rapes.

On Saturday, the government-affiliated Ethiopian Human Rights Commission said Tigrayan rebels killed scores of civilians in the Amhara region on suspicion of being informants, supporting the federal government or offering aid to federal forces.

At least 184 civilians died, the EHRC said, accusing TPLF fighters of "wilfully (killing) scores of civilians in towns and rural areas they captured".

Dozens of civilians also died due to indiscriminate shelling by both federal forces and the rebels, it added.

TPLF spokesman Getachew Reda told AFP the report was "whitewashing Abiy's crimes and blaming others for it. We won't dignify the report by response."

Abiy's government has said it is committed to holding perpetrators of abuses accountable, while the TPLF has called for independent investigations into rights violations.

As international efforts to broker a ceasefire intensify, Ethiopia on Thursday laid out conditions for possible talks with the TPLF, which has claimed major gains in recent weeks and not ruled out a march on the capital Addis Ababa.

The conditions include a halt to attacks, a TPLF withdrawal from Amhara and Afar, and recognition of the government's legitimacy.

The TPLF in turn is demanding that aid be let into Tigray. No assistance has arrived by road since October 18, and 364 trucks are stuck in the capital of Afar waiting for authorisation, according to the United Nations.

Abiy sent troops into Tigray last November to topple the TPLF, a move he said came in response to rebel attacks on army camps.

Though the 2019 Nobel Peace laureate vowed a swift victory, by late June the TPLF had retaken most of Tigray before expanding into Amhara and Afar.