WFP spokeswoman Bettina Luescher said in an email late Wednesday that 21 metric tons of “assistance” were dropped, but that the overall operation had faced “technical difficulties.”

It was not immediately clear if that meant that the airdrop had missed its target, but Luescher said: “High altitude drops are extremely challenging to carry out and take more than one trial to develop full accuracy.”

U.S. Secretary of State John Kerry and his Russian counterpart, Foreign Minister Sergey Lavrov, have held a telephone conversation to discuss issues connected with the proposed upcoming cease-fire in Syria.

A Russian Foreign Ministry statement on Wednesday said the two top diplomats “continued discussion of the modalities of this process, demanding close coordination of efforts between our countries, including in the military sphere.”

The statement says the two stressed the importance of “renewing the intra-Syrian talks about” the situation in the war-ravaged country and ways to resolve five years of violence that has killed more than 250,000 people and displaced another 11 million from their homes.

Russia’s deputy foreign minister says the United States and Russia are discussing a new U.N. resolution that would strongly back the cessation of hostilities in Syria.

The truce, proposed by Russia and U.S. is to go into effect at midnight local time on Friday.

Gennady Gatilov told reporters on Wednesday that “it would be good” if Moscow and Washington agreed on the text of the Russian-proposed resolution by Thursday. That would enable the U.N. Security Council to vote on the resolution on Friday.

U.S. officials point out that a cessation of hostilities is already enshrined in a U.N. resolution adopted unanimously in December and endorsing a peace process for Syria. However, they say they are not necessarily opposed to another one.

A new resolution would also reportedly ask the 18 key nations on both sides of the five-year-old Syrian conflict that agreed on the peace process to support implementation of the new cessation of hostilities.

—Edith M. Lederer at the United Nations.