The United States voiced alarm Friday over the escalation of violence in Yemen and urged restraint after a rebel drone attack on the country's largest airbase killed six loyalist soldiers.

The United States, which supports the Saudi-led coalition against the Huthi rebels, said it "strongly condemns" the strike on a military parade at Al-Anad air base.

The attack, which killed six and wounded at least 12 people including top commanders, came a month after the warring sides agreed at talks in Sweden on a truce in the rebel-held port of Hodeida, a key aid gateway for the country where some 14 million are on the brink of famine.

"This attack contravenes the spirit of the Hodeida ceasefire and the progress made last month at the U.N.-led talks in Sweden," State Department spokesman Robert Palladino said in a statement.

"We urge all sides to honor the commitments they made in Sweden to their fellow Yemenis by refraining from violence and provocative acts," he said.