President Biden and Russian President Vladimir Putin warned each other of the potential for a dangerous downturn in relations if the current crisis over Ukraine further escalates, but kept a pathway open for diplomacy.

In a 50-minute conference call Thursday, Mr. Biden renewed a warning to Mr. Putin that Russia would face punishing economic sanctions if Moscow turned away from diplomacy and attacked Ukraine, a senior U.S. official said.

Mr. Putin countered that such action would lead to a dangerous rupture in ties between the two countries, a Putin foreign-policy aide said.

“Our president immediately responded, saying that if the West decides ultimately under whatever conditions to introduce such unprecedented sanctions, it could lead to the total breakdown in relations between our countries,” Yuri Ushakov told reporters.

Thursday’s call came at what a senior Biden administration official described as a “moment of crisis” over Ukraine. Mr. Putin requested the call, giving him a chance to speak directly with Mr. Biden before their negotiators meet for a series of talks next month. It was the second time they talked about Ukraine this month, the previous being a two-hour call on Dec. 7.

Since the fall, Mr. Putin has ordered troops to mass near Ukraine in what U.S. and European officials say could be a prelude to an invasion. In doing so, Mr. Putin is trying to force the U.S. and its allies in the North Atlantic Treaty Organization to address Moscow’s objections to the military alliance’s ties with Ukraine, Georgia and other former Soviet states, the current and former officials said.

Both sides described the tone of Thursday’s discussion as serious and substantive. The senior U.S. official, however, said that Washington continues to monitor the deployment of Russian forces in Crimea and near Ukraine.

During the call, the U.S. official said, Mr. Biden outlined two paths that Mr. Putin faces: one of de-escalation and diplomacy, and another in which Russia takes military action against its Ukrainian neighbor and encounters a serious response from the West.

That, Mr. Biden and top officials have said, would include stringent economic sanctions, stepped up military aid to Ukraine and a reinforced U.S. military presence along NATO’s eastern flank near Russia. The Kremlin’s sharp reaction to the warning of sanctions was seen by some U.S. officials as an indication that Moscow appears to be taking that threat seriously.

Mr. Biden has rebuffed Russian demands that the U.S. call a halt to NATO’s eastward expansion and rule out potential membership for Ukraine, a position the U.S. official repeated Thursday.

“Our position is very clear,” the official said. “These are decisions to be made by sovereign countries, obviously in consultation with the alliance and not for others to determine.”

Mr. Putin sparked the current crisis, current and former U.S. officials said, with his troop deployments and demands for security guarantees that would prevent the eastward expansion of NATO and deny membership in the alliance to parts of the former Soviet Union.

“It’s almost as if Putin and the Kremlin were saying: ‘Wait a minute, we’re a nuclear superpower, pay attention to us,’” said Angela Stent, a Brookings Institution fellow and former U.S. national intelligence officer for Russia and Eurasia. “Key Western players have been distracted, and Putin took the initiative and, in essence, created a crisis where there wasn’t a crisis in order to secure concessions from the West.”