MOSCOW — A Russian court cleared the way on Saturday for the possible transfer of the opposition leader Aleksei A. Navalny to the country’s penal colony system, the latest step by authorities to silence the man who has become the country’s most vocal critic of President Vladimir V. Putin.
The court rejected Mr. Navalny’s last possible appeal before such a transfer. But it remains unclear whether or when he will leave his cell in a high-security prison in Moscow. He could be held there for further court appearances on other pending legal matters.
Mr. Navalny was detained in January upon returning from Germany, where he was being treated for a near-lethal poisoning with a nerve agent last year — an act that he and Western governments blamed on the Kremlin. He returned despite knowing that his homecoming would almost surely land him in prison, a challenge that gave rise to mass street protests in support of him.
The ruling, which was expected, upheld Mr. Navalny’s sentence of more than two years in prison and set Russia on a collision course with Western nations, which could impose additional sanctions on Moscow. On Tuesday, the European Court of Human Rights, whose jurisdiction is recognized by Russia, ruled that Mr. Navalny must be released immediately from prison.
The Kremlin’s spokesman, Dmitri S. Peskov, rejected that demand and called the Strasbourg-based court’s ruling “a serious attempt to intervene in internal judicial matters of Russia.”
In his final argument in court on Saturday, Mr. Navalny quoted from the Bible, saying that truth would triumph. He also told his followers not to feel deserted.
“Our government is trying to convince people that they are all alone,” he said.
Over the past month, Mr. Navalny’s allies have organized two countrywide protests in his support that drew tens of thousands to the streets. The police arrested thousands.
The poisoning, the sentencing and the crackdown on protesters all signaled a pivot by Mr. Putin to harder-line domestic policies. Mr. Navalny had been jailed frequently before, but only for brief stints in Moscow, and he has never been sent to a penal colony.
Under Russia’s criminal justice system, transferring an inmate to the penal colonies is a lengthy process of travel on a specialized prisoner train wagon. It can begin at any point after a court rejects the first appeal of a sentencing, which happened on Saturday.
The trip can take weeks, with stops at transfer prisons, during which inmates are generally not allowed to contact lawyers or family members. Their destination sometimes remains unknown until they arrive.
Mr. Navalny can petition the European Court of Human Rights on grounds that its demand to release him has gone unheeded. Although the court cannot legally compel Russia to abide by its ruling, the dispute could escalate to the European Council, the political body that comprises the leaders of European Union member states. It could also potentially lead to Russia’s expulsion or withdrawal from that group.
It would be a significant breach. Russia joined the Council in 1996, signaling an end to the Cold War division of Europe on human rights issues.
Andrew E. Kramer contributed reporting.