GENEVA (AP) — The U.N. envoy for Syria appealed to the U.S. and Russia to intervene to help revive Syrian peace talks that sputtered to a pause Wednesday, saying a recent spike in fighting has overshadowed the talks and put an increasingly feeble truce in "great danger."

Staffan de Mistura spoke to reporters early Thursday after briefing the U.N. Security Council via videoconference about the largely stalled indirect talks between the Western- and Saudi-backed opposition and envoys from President Bashar Assad's government, which has the backing of Moscow.

De Mistura said he hoped that the talks would resume in May, and he predicted the overall process would continue as previously planned through July. But stopped short of setting a specific date, pointing to recent upsurge in fighting, notably in and around Syria's largest city of Aleppo.

De Mistura lamented the worsening violence, saying that "in the last 48 hours, we have had an average of one Syrian killed every 25 minutes, one Syrian wounded every 13 minutes ... How can you have substantial talks when you have only news about bombing and shelling?"

Speaking at the end of a third session of Syria peace talks this year, de Mistura said a truce brokered by the U.S. and Russia had pulled off a "miracle" by sharply reducing violence in March, but acknowledged that the renewed fighting has put the truce "in great danger."

He called for a "US-Russian initiative at the highest level" to help reinforce it.

"There is no reason that both of them — who have been putting so much political capital in that success story and have a common interest in not seeing Syria ending up in another cycle of war — should not be able to revitalize what they created, and which is still alive, but barely," he said of the two countries.

The talks foundered last week after the Western- and Saudi-backed opposition called the High Negotiations Committee suspended formal participation in the indirect talks with Assad's envoys to protest alleged government cease-fire violations, a drop in humanitarian aid deliveries and no progress in winning the release of detainees in Syria.

De Mistura suggested back-channel work between Moscow and Washington was already under way to help the truce, and that a revival of it would help bring the two sides back to the table.

"I know that both the Russian Federation and the U.S. are talking among themselves on how to salvage on what has been actually a remarkable success — but needs to be sustained," he said, referring to the cease-fire. If it is revived, he predicted: "It will not be difficult for everyone to come back around the table."