"They are killing our people in this country, they are killing children, all ages of the population and they are conducting rape," Debretsion told CNN in a phone interview from an undisclosed location.
"All sorts of acts of genocide have been committed in Tigray. So, the most important thing is that an investigation must be conducted," he added.
"We are calling for an investigation into the CNN findings on the ground in Tigray."
Ethiopia's foreign ministry on Monday rejected a call from the United States for the Ethiopian federal government to pull forces out of Tigray, saying it was "regrettable" that the US had attempted "to make pronouncements on Ethiopia's internal affairs and specifically, the reference to the Amhara regional forces redeployment."
"It should be clear that such matters are the sole responsibility of the Ethiopian government, which as a sovereign nation, is responsible to deploy the necessary security structures and means available in ensuring the rule of law within all corners of its borders," the ministry said in a statement.
US Secretary of State Antony Blinken said Saturday that the US was "gravely concerned by reported atrocities and the overall deteriorating situation," and called for Eritrean and Amhara regional forces to withdraw immediately. Blinken's statement came one day after CNN's investigation, as well as another by Amnesty International, both detailing eyewitness accounts of civilian massacres in two separate assaults in late 2020.
Eritrea's government denied involvement in the atrocities reported by Amnesty, but has yet to respond to CNN's request for comment in relation to the Dengelat massacre.
Debretsion said he was making an urgent call to the Biden administration to keep the pressure on the Ethiopian and Eritrean governments.
"We want to have peace in this region, in this country so we want [the US] to continue to push [for the withdrawal] of invader forces from Tigray to stop the atrocities, genocide and destruction," he told CNN.
"We need, you know, humanitarian assistance as well ... The whole Tigray is in social and economic crisis. Our people need assistance, they need humanitarian support. So, it's an urgent call. We need this push from the [US] President."
Repeated denials of Eritrean involvement
The Amnesty International report charged that Eritrean forces killed hundreds of unarmed civilians in the city of Axum, also in Tigray region, in November through indiscriminate shelling and shooting and extrajudicial killings, in what the human rights organization said could amount to a crime against humanity.
The Ethiopian foreign ministry's statement Monday did not mention the presence of forces from neighboring Eritrea during the recent offensive. It added that it was "fully committed" to investigating any human rights violations. Prime Minister Abiy has also denied that soldiers from Eritrea crossed into Tigray to support Ethiopian forces.
Blinken had called for a "full, independent international investigation into all reports of human rights violations, abuses and atrocities."
"We strongly condemn the killings, forced removals and displacements, sexual assaults, and other extremely serious human rights violations and abuses by several parties that multiple organizations have reported in Tigray," he said.
Blinken also acknowledged Abiy's stated commitment to allow humanitarian aid to the region, and said that the US Agency for International Development would send a disaster assistance response team to Ethiopia. On Monday, Ethiopia's foreign ministry said it was working to ensure unfettered access to Tigray for the delivery of humanitarian assistance.
TPLF troops seized power in Ethiopia in 1991 with the backing of Eritrea, and the TPLF's Meles Zenawi became the nation's leader. Debretsion became deputy prime minister after Zenawi's death in 2012. The TPLF ruled until 2018, when members of the Oromo and Amhara ethnic groups united against the party. Abiy was appointed prime minister in 2018 and won a Nobel prize last year for his peace deal with Eritrea.
Violence flared in the region last year after Tigray went ahead with local elections that the Abiy government had banned because of the pandemic.
An earlier version of this story incorrectly stated the year Debretsion became Deputy Prime Minister. It was in 2012.