ADDIS ABABA (Reuters) - A powerful party in Ethiopia’s government accused authorities of arresting members of its ethnic group in a politically-driven crackdown - an unprecedented public charge exposing deep rifts at the heart of the ruling elite.

The accusation marked growing tensions between elements in the Tigrayan People’s Liberation Front (TPLF) - a movement that has dominated Ethiopia for decades - and new reformist prime minister Abiy Ahmed who has upended politics with a string of radical reforms.

At least 79 security officers, officials, businessmen and women, many of them Tigrayan, have been arrested since last week - under what the government said was a clamp-down on corruption and mistreatment of prisoners.

Amnesty International and other rights groups have welcomed the arrests. But TPLF chair Debretsion Gebremichael said on Monday the arrests ordered under “the pretext of corruption and human rights are being used to attack Tigrayans”.

The prime minister’s office did not immediately respond to a request for comment on Debretsion’s remarks.

Abiy’s rise - as Ethiopia’s first leader from the majority Oromo group - had transformed decades-old hierarchies in the Ethiopian People’s Revolutionary Democratic Front (EPRDF) coalition that was founded by the TPLF and came to power in 1991.

Soon after Abiy was inaugurated in April, he made peace with long-time foe Eritrea and started pushing reforms he said were meant to rein in the military and security services and limit their involvement in the economy - changes that have been largely welcomed by Western powers.

The TPLF’s Debretsion did not spell out who he thought was behind the arrests, that were announced by the government’s attorney general. “There is a foreign involvement in the process. Thus, it is unacceptable,” he said, without giving further details.

Debretsion picked out last week’s arrest of Kinfe Dagnew, a Tigrayan major general in the army and former chief executive of the METEC military-led conglomerate.

“While Kinfe was arrested peacefully, they tied him handcuffs. This is a political attack,” Debretsion told a news conference.

“While they should have gone after an individual, they went after an ethnic group and a party,” he said in comments aired by Dimtsi Woyane TV.

Kinfe and others appeared in court but have not been charged or entered any pleas. There have been no statements from them or lawyers representing them.