A missile strike on a Doctors Without Borders clinic in Yemen killed at least four people Sunday, the group said, condemning what it called a "worrying pattern" of such attacks.
The Paris-based medical humanitarian organisation said three of its staff members were among 10 people wounded in the raid, the third of its kind in four months in the war-ravaged country.
Two other members of staff were in "critical condition", the group known by its French acronym MSF said in a statement.
"The numbers of casualties could rise as there could still be people trapped in the rubble," it said, adding the missile hit the medical facility in the Razeh district of Saada province.
But all staff and patients had been evacuated, with the patients being transferred to another MSF-supported hospital in Saada, it said.
MSF could not specify whether the medical facility was hit in an air strike by the Saudi-led coalition or by a rocket fired from the ground.
Its director of operations, Raquel Ayora, denounced the strike and repeated that the organisation constantly shares the coordinates of its facilities with those fighting in Yemen.
"All warring parties are regularly informed of the GPS coordinates of the medical sites where MSF works," said Ayora.
"There is no way that anyone with the capacity to carry out an air strike or launch a rocket would not have known" that the clinic was a functioning health facility supported by MSF, Ayora said.
"We strongly condemn this incident that confirms a worrying pattern of attacks to essential medical services and express our strongest outrage as this will leave a very fragile population without healthcare for weeks," said Ayora.
"Once more it is civilians that bear the brunt of this war," she added.
Saada is the heartland of the Iran-backed Shia Houthi rebels that the coalition has been bombing since March in support of Yemen's beleaguered government.
MSF last month accused the coalition of bombing its clinic in Taez, southwest Yemen, wounding nine people including two staff members.
The coalition said it would investigate that claim although it has repeatedly insisted that it does not attack civilians.
In October, air strikes hit another hospital run by MSF near Saada without causing any deaths.
More than 5,800 people have been killed in Yemen since March, about half of them civilians, according to the United Nations.
At least 27,000 people have been wounded as 80 percent of the population is in need of humanitarian aid, according to UN figures.
The UN envoy for Yemen, Ismail Ould Cheikh Ahmed, arrived Sunday in Sanaa in a bid to convince the rebels and their allies to attend a new round of peace talks.
"We are in Sanaa to exert more efforts with all parties concerned to (convince them to) hold a new round of talks," the rebel-controlled sabanews.net website quoted the envoy as saying upon his arrival in the rebel-held capital.
The UN envoy had met with Yemeni government officials temporarily based in Riyadh, before he headed to Sanaa.
Foreign Minister Abdel Malak al-Mekhlafi told AFP the talks, initially scheduled to start on January 14 had been postponed until January 20 or 23.
The government sat down with the rebels and their allies last month in Switzerland for six days of talks that ended without a major breakthrough.
Also on Sunday, Yemeni intelligence colonel Ali Saleh al-Nakhibi was shot dead by unidentified gunmen in second city Aden, a security official said.