A Yemeni colonel loyal to former president Ali Abdullah Saleh and two rebels have been killed in clashes, Saleh's party and a news agency said Sunday, in an unprecedented escalation of violence between the allies.

Col. Khaled Al-Rida was killed in clashes in the rebel-held capital Sanaa late Saturday, a statement released by Saleh's General People's Congress party said.

Rida was the deputy head of foreign relations in the party.

While the statement did not name the Houthi rebels, it accused a "group that knows no morality or oaths" of being behind the killing — a thinly-veiled reference to the Houthis, who over the past week have lashed out at Saleh as a "back-stabber" and "traitor" as tensions rise within the rebel alliance.

The rebel-run Saba news agency said two members of the Popular Committees, a tribal alliance largely dominated by the Houthis, were killed late Saturday in Sanaa.

A source within the GPC said the clashes erupted at a rebel checkpoint in the southern neighborhood of Hadda after a dispute between fighters manning the checkpoint and armed supporters of Saleh who were driving by.

Saleh and his one-time foe Abdul Malik Al-Houthi joined ranks in 2014 in a shock alliance that drove the internationally recognized government out of Sanaa and into the southern province of Aden.

A war of words between Saleh and rebel leader Houthi has escalated in the past week.

The two have publicly accused each other of treason, with Saleh hinting his allies were merely "a militia" and the rebels warning the former president he would "bear the consequences" of the insult.

The Houthis reportedly suspect Saleh has been negotiating with a Saudi-led military coalition that supports the Yemeni government.

Saleh, meanwhile, is said to be displeased with the Houthis' newfound power in the capital, where they run a number of key offices.

The war between the government of President Abedrabbu Mansour Hadi, backed by the coalition, and the rebel camp has killed more than 8,300 Yemenis since 2015 and pushed the country to the brink of famine.