Russia rejects calls for a cease-fire to enable evacuations, saying Ukraine only wants time to arm.

Russia rejected calls for a cease-fire to allow for civilian evacuations in Ukraine on Tuesday, saying that requests to pause the fighting were not sincere and would only provide time to arm Ukrainian fighters.

The rejection, delivered at a United Nations Security Council meeting on Ukraine, came just hours after the U.N. secretary general, António Guterres, called for a four-day cease-fire to allow for evacuations in battle zones and safe corridors to bring in food and medicine.

Civilians, including children, remain trapped in the eastern Ukraine region of Donbas, where Russia has begun a new and more fierce offensive, as well as in the devastated port city of Mariupol, where Ukrainian defenders are making a last stand from the bunkers of a steel complex.

Dmitry Polyanskiy, Russia’s deputy U.N. ambassador, told the Security Council that calls for his country to establish humanitarian cease-fires were “insincere, and in practice they merely point to an aspiration to provide Kyiv nationalists breathing room to regroup and receive more drones, more antitank missiles and more MANPADS.” He was referring to man-portable air-defense systems, which are essentially highly mobile surface-to-air missiles.

Earlier, Mr. Guterres had said that more than 12 million people in Ukraine now needed humanitarian assistance but that the number was expected to rise to 15.7 million, or about 40 percent of all Ukrainians remaining in the country. Millions have fled abroad, and many others are internally displaced.

Even China, which has not condemned Russia and has abstained from votes on resolutions against it, said it supported a humanitarian cease-fire and called on Russia and Ukraine to move toward that goal.

The reality gap between Russia and the majority of Security Council members and U.N. officials remained on display. Two U.N. officials and diplomats representing Eastern European countries hosting millions of Ukrainian refugees laid out the challenges of the situation, which Russia dismissed, saying that Ukraine had been plagued by migration of its citizens for years.

Some statements from U.N. officials and diplomats on Tuesday spoke to growing frustration at their inability to broker a cease-fire, mediate a peace deal or convince Russia to end its aggression.

“Colleagues, it appears that these meetings do not affect much either the security situation on the front line or the humanitarian situation in Ukraine,” Ukraine’s ambassador, Sergiy Kyslytsya, said.

Russia, as a permanent member of the Security Council, has veto power and has used it twice on resolutions focused on Ukraine since Russia’s invasion in February. But even diplomatic attempts spearheaded by the U.N.’s top humanitarian chief, Martin Griffiths, who had traveled to Russia and Ukraine last week, failed.

“So while we will continue our job to deliver aid, we need this council to do its job too,” said Kelly Clements, deputy high commissioner for U.N.’s refugee agency. “We therefore call on all of you in this council again — and yes, we are aware of the deep divisions — to put aside your differences and find a way to end this horrific and senseless war.”