Nearly 50 civilians were killed in missile strikes on hospitals and two schools in northern Syria on Monday, the United Nations said, deepening the country’s humanitarian crisis despite plans for a temporary cease-fire later this week.

Doctors Without Borders said that at least seven people were killed early Monday when rockets hit a clinic that it supports in Idlib province. The group also said eight people were missing in what it called a “deliberate attack” on its facilities.

Doctors Without Borders did not say which group or military had fired the rockets; rights groups have documented numerous Russian and Syrian government strikes on hospitals and medical facilities across the country. In total, at least five medical facilities and two schools in Idlib and neighboring Aleppo province were attacked Monday, a U.N. spokesman said.

State Department spokesman John Kirby said Monday’s carnage “casts doubt on Russia’s willingness and/or ability” to stop the Syrian government from carrying out strikes on civilian targets.

People carry a stretcher amidst debris after a hospital supported by Doctors Without Borders (MSF) was hit by suspected Russian airstrikes near Maaret al-Numan, in Syria's northern province of Idlib, on February 15, 2016. (Omar Haj Kadour/AFP/Getty Images)

In a statement Monday, Kirby urged “the cessation of hostilities that the Syrian people desperately need.”

The fresh fighting comes after Syrian regime forces — backed by Russian warplanes, Iranian troops and Iraqi militia fighters — have made significant gains against rebel forces in northern Syria in recent weeks. The advances have raised the stakes of the nearly five-year-long conflict, which already has transformed into a proxy war.

Last week, Turkey and Saudi Arabia, which have supported the Syrian rebels, said that they planned to intensify strikes on the Islamic State in Syria and that they were also considering deploying ground troops to the country. Turkish and Saudi officials walked back those statements on Monday after U.S. diplomats called for calm.

“It’s not true,” Turkish Defense Minister Ismet Yilmaz said Monday of reports that Turkey had already sent in a limited number of troops.

Syria’s state-run Syrian Arab News Agency published a letter from the country’s foreign ministry to the U.N. Security Council over the weekend. It claimed that Turkish forces were among 100 gunmen that entered the country Saturday in an operation to support anti-government rebels.

“There is no thought of Turkish soldiers entering Syria,” Yilmaz said, according to Turkey’s state-run Anadolu Agency.

Saudi Foreign Minister Adel al-Jubeir also said late Sunday that the decision to deploy ground troops is up to the U.S.-led coalition battling the Islamic State.

“The timing is not up to us,” Jubeir said from the Saudi capital, Riyadh.

But Turkey, which shares a long border with Syria, has vowed to prevent Syrian-Kurdish militias from seizing more territory that they could use for a future state. And Saudi Arabia has already been worried about growing Iranian influence in the region, analysts say.

A Saudi diplomat said Sunday that Saudi Arabia was “very serious” about sending ground troops into Syria but that it will wait to see whether plans for a pause in hostilities agreed on by the United States and Russia transpires later this week.

The diplomat, who spoke on the condition of anonymity because of the sensitivity of the topic, said the “disarray” on the Syrian battlefield spurred Saudi to action. He added that Riyadh wanted to counter Islamic State militants and Iranian influence in the country.

“Time is running out,” he said. “We are waiting for the peace process to end. We believe it will fail, and when it does, the situation will be completely different.”

He said Saudi officials discussed the possibility of sending troops with Turkish Prime Minister Ahmet Davutoglu during a recent three-day visit to Saudi Arabia. Yilmaz confirmed that a decision had been reached for Saudi Arabia to send four F-16 fighter jets to Turkey’s Incirlik air base.

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Cunningham reported from Cairo.