President Vladimir V. Putin of Russia gave an ominous warning on Thursday to protesters in Belarus not to push too hard to topple their country’s embattled president, saying that Russia had formed a special reserve force of security officers to restore order in the event of chaos in its western neighbor.

Mr. Putin, speaking in an interview with Russian state television, said he had ordered the creation of a “certain reserve of law enforcement officers” at the request of Belarus’s authoritarian leader, Aleksandr G. Lukashenko. He said the force had not been deployed yet, because “we also agreed that it will not be used unless the situation gets out of control.”

Mr. Putin’s remarks sent the strongest warning yet that Russia could use force to halt more than two weeks of protests in Belarus, which he described as “perhaps the closest country to us.” While saying that Belarusians themselves must decide their future after a disputed presidential election on Aug. 9, he added, “We are certainly not indifferent to what is happening there.”