Russia is gathering thousands of troops, as well as artillery and other equipment, at its border with Ukraine as part of military training exercises that also serve as a blunt reminder of Russia’s ability to easily move deeper into the neighboring country.

The exercises are set to take place over the next two weeks amid a standoff with the United States and Europe over the fate of Ukraine’s autonomous Crimea region, currently occupied by Russian troops.

Lawmakers in Crimea have scheduled a referendum Sunday on whether the region should secede from Ukraine and join Russia. President Obama and European leaders have promised economic and diplomatic retaliation if that happens.

In a bid to defuse the growing tension and seek a diplomatic resolution, Secretary of State John F. Kerry headed to London to meet with Russian Foreign Minister Sergei Lavrov on Friday.

At the United Nations, Russian envoy Vitaly Churkin defended Crimea’s right to hold a referendum on its future. Asked by Ukraine’s new prime minister, who was at the United Nations on Thursday, whether Russia was seeking war, Churkin responded: “Russia does not want war and neither do the Russians, and I’m convinced the Ukrainians don’t want that either.”

The U.S. ambassador to the United Nations, Samantha Power, assailed Russia for pursuing a “course of military action from the outset” in Ukraine and pleaded with Russian authorities to reduce tensions by holding direct talks with officials in Kiev — which Russia has resisted doing.

“This is the moment to show that laws matter, rules matter, territorial integrity matters. If we don’t come together, if we don’t send a clear signal of our shared commitments, we will live with the consequences in Crimea, and well beyond,” she said.

The Russian Defense Ministry reported on its Web site Thursday that 1,500 paratroopers would be dropped along with their equipment into the Rostov region near the border with Ukraine for exercises over the next two weeks.

In the past few days, Russian armored vehicles have been spotted in Belgorod, farther to the north. The Defense Ministry said the exercises include 8,500 artillery troops, along with an assortment of rocket launchers, howitzers, antitank guns and other weapons.

“The main goal of the ongoing events is to comprehensively assess the units’ teamwork and subsequently tackle combat training tasks on an unfamiliar terrain and untested training ranges,” the ministry said in a statement.

Russia offered the description of its military movements a day after Ukrainian officials complained of a military buildup along their country’s borders.

In Washington, a senior U.S. official said the United States is closely watching the hastily called Russian military exercises and considers them a potential threat.

“It’s the second time in a week” that Russian troops maneuvered near the border under the guise of exercises, said the official, who spoke on the condition of anonymity to discuss the sensitive matter.

Although the exercises are not confined to the Ukraine border region — they will also be conducted in central Russia — the signal is a strong one.

“In general terms, this is what a military does if it wants to keep at readiness,” said Mark Galeotti, a New York University professor who studies Russian security. “But in circumstances like this, they’re very aware of the political implications of any movements.”

Galeotti, who is in Moscow, said that paratroopers are mobile and good at sealing off an area, but that they would need regular troops to back them up quickly if serious conflict arose. “What they are not good at is relatively hard-core military combat,” he said.

The crisis over Crimea, a region with strong ties to Russia, has developed into perhaps the worst standoff between Russia and the West since the end of the Cold War. It began last month when the pro-Russian government of Ukrainian President Viktor Yanukovych was toppled after mass protests and new leadership took over with the blessing of European nations and the United States.

Russia promptly moved troops into Crimea and is hosting Yanukovych, who has vowed to reclaim power.

Dozens of protesters were killed during the demonstrations that brought down Yanukovych, and supporters of the new government and pro-Russian factions have clashed often since then. On Thursday, a man was stabbed to death in the eastern city of Donetsk in fighting between several hundred people chanting slogans praising Russian President Vladimir Putin and a similar-size crowd condemning Moscow’s takeover of Crimea, the Reuters news agency reported. The local health authority said more than a dozen people were taken to a hospital and treated for injuries.

Before leaving for London, Kerry told the Senate Appropriations subcommittee on foreign operations that he does not know whether Russian annexation is a foregone conclusion, but he acknowledged “strong indications” that former defense secretary Robert M. Gates is right in saying that Crimea is now lost to Ukraine.

“There are other . . . thoughts out there that suggest that something short of a full annexation might also be achievable,” Kerry told the panel.

Obama met with Ukraine’s interim prime minister, Arseniy Yatsenyuk, at the White House on Wednesday and said the United States and its allies would “apply a cost” to Russia if it tries to split Crimea from the rest of Ukraine.

German Chancellor Angela Merkel emphasized the point in a speech Thursday to the German Parliament that recalled Europe’s centuries of strife over “spheres of influence and territorial claims,” news services reported from Berlin.

“I’m afraid we have to dig in for the long haul to solve this conflict,” she said, with sanctions against Russia expected early next week if the Sunday secession vote proceeds.

“If Russia continues on the course of the last weeks, it won’t just be a catastrophe for Ukraine,” Merkel said. “It would also cause massive economic and political harm to Russia.”

Pro-Russia forces on Thursday continued efforts to take control of Ukrainian military facilities in Crimea. About 100 armed militiamen from self-defense units arrived by bus at an oil warehouse on a base near the train station in the region’s capital, Simferopol, said Vladislav Seleznyov, a spokesman for the Ukrainian military.

In a separate incident, he said, a Russian navy ship was scuttled at the entrance to the bay at Donuzlav in northern Crimea, blocking Ukrainian navy ships from leaving. It was the third ship deliberately sunk to impede naval traffic, he said.

Morello reported from Sevastopol, Crimea. Anne Gearan in Washington contributed to this report.