Humanitarian aid supplies are unloaded from a Czech military airplane into a Syrian Arab Red Crescent truck, after it landed in Damascus airport on June 5. On June 1, a government siege of a Damascus suburb, Darayya, was lifted and medical supplies were allowed to be trucked in. (Omar Sanadiki/Reuters)

Syria has given initial approval for humanitarian aid convoys to 17 areas where civilians are encircled by government forces, the United Nations said Thursday. All of the deliveries are to take place before the end of June.

U.N. envoy Staffan de Mistura, who announced the approval in Geneva, noted that similar approvals in the past frequently have been rescinded or compromised. He said that the World Food Program has completed a plan for airdrops or landings of food and medical supplies to hundreds of thousands of people in besieged areas and that they are “still an option” if land convoys do not succeed.

But de Mistura acknowledged that airdrops, as well as land deliveries, “need government permission.”

“To my knowledge, there is no place inside Syria that does not require the permission” or risk confrontation with Syrian air defenses, he said. Without such approval, those governments that have demanded humanitarian access — led by the United States and Russia — “will have to take up their own decision and see what to do about it.”

Following a Security Council meeting last week, the United Nations on Sunday officially asked Syria for airdrop permission, which de Mistura indicated had provided leverage for ­preliminary government agreement — which must be followed by written approval — on the land convoys.

“In the next few hours,” he said, “we hope to see some of that approval to actually become concrete. That is the test, of course, as always.”

In a news conference that included “bad news,” de Mistura said that in Darayya, a government-besieged suburb of Damascus that has been without food deliveries for four years, a mosque had been “heavily shelled.” That begged the question, he said, of whether it was “true that whenever there is an approval” by the government, “there is also a punishment. Because it is not the first time that there has been this type of incident.”

Continued back-and-forth on humanitarian issues came amid further deterioration in a partial cease-fire in Syria’s civil war begun in late February. De Mistura referred to renewed “heavy bombing of hospitals,” particularly children’s hospitals in Aleppo. The Syrian government this week said it was launching a new offensive to retake Aleppo from rebel forces that have partially occupied it for years.

Russia has said that it will renew its air attacks on behalf of the government to help close the remaining land route, north of Aleppo, for rebel supplies from Turkey. Russia and Syria have claimed that the route is being used by “terrorists.” The United States and other opposition supporters have acknowledged some operational and geographical overlap between Jabhat al-Nusra, al-Qaeda’s Syrian affiliate, and rebel forces but have charged Russia and Syria with using that as an excuse to bomb the opposition.

Opposition political leaders have said they will not return to U.N.-led talks with the government in Geneva until the cease-fire and humanitarian and other demands are met.

De Mistura said Thursday that the “time is not yet mature for [an] official third round of the intra-Syrian talks. We are intending, and we want to do it as soon as possible.”

The talks, which began in conjunction with the cease-fire, initially set Aug. 1 as a deadline for completion of plans to install a transition government in Syria. While that is still “attainable,” de Mistura said, “this is not yet the moment” to restart the talks.

The opposition has also demanded that Syrian President Bashar al-Assad release political and other prisoners his government is holding. De Mistura said he had received information from “one main source” that “a substantial number of fighters appeared to have been released,” but did not have confirmation or details.