“You are as exposed to attack if you go to a hospital as anywhere else, some would say more so,” Mr. Egeland said.
Both the Syrian and Russian governments have said their forces are attacking only militants.
But at least two medical facilities serving thousands of patients in Idlib were struck in nine attacks on medical centers or medical workers in Idlib and Eastern Ghouta in the last eight days, Mr. Egeland said. These attacks followed more than 100 attacks on medical facilities recorded by international agencies in 2017, he added.
Mr. Egeland said the proposed humanitarian pause in intense fighting around Eastern Ghouta would allow delivery of food for a population that has been cut off from relief for years and is suffering acute malnutrition.
Bombing and shelling of Eastern Ghouta have killed at least 85 civilians and wounded 183 since the start of the year, the top United Nations human rights official, Zeid Ra’ad al-Hussein, said on Wednesday. Aircraft bombed two medical facilities, killing a medical worker in that period, he said.
Opposition forces in Eastern Ghouta have fired on residential areas of Damascus since Jan. 1, inflicting civilian casualties, Mr. al-Hussein added, citing a rocket attack last week.
“The situation is screaming for a humanitarian pause in the extremely intense fighting so that humanitarian agencies can do their work and civilians can get relief,” Mr. Egeland said.
The appeal came as Mark Lowcock, the United Nations emergency relief coordinator, visited Damascus to press the case for unfettered access by relief agencies to millions of civilians in need of aid and for the evacuation of civilians who require urgent medical treatment.
A temporary deal struck between the government and rebels in Eastern Ghouta led to the evacuation of 30 critically ill patients between Christmas and New Year’s Day, and international agencies have confirmed that they are receiving medical care in Damascus hospitals, Mr. Egeland said.
But the Syrian government has not responded to repeated appeals by the United Nations since September for evacuation of other Eastern Ghouta civilians in need of medical attention. Mr. Egeland said more than 500 people required urgent evacuation.
After two days of talks in Damascus, Mr. Lowcock said on Thursday that he hoped for a number of positive developments “soon” on measures to relieve humanitarian suffering, but that more discussions would be needed.
Russia, the main ally of President Bashar al-Assad of Syria, has repeatedly said in recent months that it is winding down military activities in the country’s nearly seven-year-old war. But the offensive aimed at insurgents in Idlib appeared to suggest otherwise.
Part of Russia’s aggressive response in Idlib may reflect anger over an attempted armed drone assault on Russian bases in Syria last weekend. The Russian Defense Ministry said the 13 drones, which were either shot down or crashed before reaching their targets, had been launched by insurgents in Idlib.
At a Defense Ministry briefing in Moscow on Thursday, officials suggested that the explosives carried by the drones may have been manufactured in Ukraine. There was no immediate comment from Ukrainian officials about that assertion.
The increased fighting in Idlib has put at risk an effort by Russia to convene a meeting of Syrian adversaries in the Russian city of Sochi at the end of this month.
Turkey, which backs some insurgent groups fighting Mr. Assad but has been collaborating with his allies, Russia and Iran, on efforts to stop the fighting, insisted this week that the bombing attacks in Idlib must stop, the Turkish news media reported.
Mevlut Cavusoglu, the Turkish foreign minister, said Mr. Assad’s forces were responsible for most of the fighting in Idlib, and could “negatively affect efforts to launch a process for a political settlement.”