The coalition has said it was not behind Friday's attack on a detention centre in the rebel heartland of Saada which Doctors Without Borders (MSF) said killed at least 70 people.

But the Joint Incidents Assessment Team (JIAT), which the coalition set up but says operates independently, said it was following up on the matter, according to the official Saudi Press Agency.

"From the first hours after news of the incident broke, the relevant team began investigation procedures and collecting data and documents pertaining to it," it said.

"The results will be announced as soon as the investigation wraps up."

The Saudi-led coalition intervened in the Yemeni civil war in 2015 to support the government against the Iran-backed rebels.

MSF accused the coalition of behind Friday's attack, which the Huthis said killed at least 91 people and wounded more than 200.

"There is no way to deny that this is an air strike, everyone in Saada city heard it," an unnamed member of the aid agency was quoted as saying in a statement late on Saturday.

On Wednesday, human rights group Amnesty International said the coalition "used a precision-guided munition made in the United States" in the strike that hit the prison.

The conflict, which erupted in 2014, has killed hundreds of thousands of people directly or indirectly and left millions on the brink of famine, according the United Nations which calls it the world's worst humanitarian crisis.