POTI, Georgia — Russian soldiers took about 20 Georgian troops prisoner at a key Black Sea port at western Georgia today, blindfolding them and holding them at gunpoint, and commandeered American Humvees awaiting shipment back to America.

The move came as a small column of Russian tanks and armored vehicles left the strategic Georgian city of Gori in the first sign of a Russian pullback of troops from Georgia after a cease-fire intended to end fighting that reignited Cold War tensions. The two countries today also exchanged prisoners captured during their brief war.

However, Russian soldiers took Georgian servicemen prisoner in Poti — Georgia’s key oil port city — and commandeered the American Humvees.

Russian forces blocked access to the city’s naval and commercial ports on Tuesday morning and towed the missile boat Dioskuria, one of the navy’s most sophisticated vessels, out of sight of observers. A loud explosion was heard minutes later.

Several hours later, an Associated Press photographer saw Russian trucks and armored personnel carriers leaving the port with about 20 blindfolded and handcuffed men riding on them. A port spokesman, Eduard Mashevoriani, said the men were Georgian soldiers.

A pentagon spokesman, Bryan Whitman, said officials were looking into the reported theft of the Humvees.

The deputy head of Russia’s general staff, Colonel General Anatoly Nogovitsyn, said Russian forces plan to remain at Poti until a local administration is formed, but did not give further details. He also justified previous seizures of Georgian soldiers as necessary to crack down on soldiers who were “out of any kind of control … acting without command.”

An AP television crew has seen Russian troops in and around Poti all week, with local port officials saying the Russians had destroyed radar, boats and other Coast Guard equipment there.

Russian troops last week drove Georgian forces out of South Ossetia, where Georgia on Aug. 7 launched a heavy artillery barrage in the separatist Georgian province with close ties to Russia. Fighting also has flared in a second Russian-backed separatist region, Abkhazia.

The short war has driven tensions between Russia and the West to some of their highest levels since the breakup of the Soviet Union, but President Medvedev has icily defended Russia’s actions.

“Anyone who tries anything like that will face a crushing response,” he said yesterday. Later Mr. Medvedev handed out military medals to Russian soldiers involved in the fighting.

The cease-fire requires both sides to return to positions held before the fighting began, but Mr. Whitman said this morning at Washington that it didn’t appear Russia had made any significant withdrawal of forces.

“So far we have not seen any significant movement out of Georgia,” he said.

At central Georgia today, a small column of Russian tanks and armored vehicles left Gori, and a Russian officer said they were heading back to South Ossetia and then Russia. A Russian military officer at the scene, Colonel Igor Konoshenkov, gave no timetable for when the unit would reach Russia.

At an emergency meeting at Brussels, Secretary of State Rice and her 25 NATO counterparts demanded that Russia immediately withdraw its troops from Georgia, an American ally that wants to join NATO. NATO allies insisted that Georgia remains on track to join NATO despite Moscow’s opposition.

The NATO foreign ministers announced today that the alliance “cannot continue with business as usual” with Russia as long as its troops remain at Georgia.

Ms. Rice said that the emergency meeting of NATO foreign ministers sent a message that Russia could not draw new dividing lines in Europe.

“A new line in Europe where Russia somehow asserts that there are those who cannot opt for a trans-Atlantic future is unacceptable,” she told a news conference.

“It is time for the Russian president to keep his word to withdraw Russian forces,” Ms. Rice said.

NATO’s secretary-general, Jaap de Hoop Scheffer, said “the future of our relations will depend on the concrete actions Russia will take to honor the words of Mr. Medvedev to abide by the six-point peace plan, which is not happening at the moment.”

France and some other allies had seemed reluctant to back an American hard line against Moscow before the meeting, but Foreign Minister Bernard Kouchner expressed exasperation at Russia’s failure to pull back its troops in line with the peace deal brokered last week by President Sarkozy.

Mr. Kouchner said Mr. Sarkozy may call an emergency European Union meeting to review EU relations with Russia if the troops were not pulled back to their pre-conflict positions. Mr. Kouchner warned the EU could also withdraw its backing for Russian membership of the World Trade Organization.

“It’s a possibility, among others,” Mr. Kouchner said. “We don’t want to use this sort of pressure, but we also don’t want this document (the peace deal) to remain a dead letter.”

Also today, Russia and Georgia exchanged 20 prisoners of war in an effort to reduce tensions. Two Russian military helicopters landed at the village of Igoeti, the closest that Russian forces have advanced to the Georgian capital of Tbilisi. Soldiers and men in unmarked clothing got off and two people in stretchers were taken to Georgian officials.

Georgian ambulances later brought two other people to the Russian choppers. One was on a gurney.

The Georgian Security Council head, Alexander Lomaia, told reporters at Igoeti that 15 Georgians and five Russians were exchanged. “It went smoothly,” he said. The operation also witnessed by Russian Major General Vyacheslav Borisov, who commands troops in the area.

Mr. Lomaia said the exchange removed any pretext for Russians to keep holding positions at Igoeti, 30 miles west of Tbilisi, or anywhere else on Georgia’s only significant east-west highway.

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Associated Press writers David Nowak, Jim Heintz and Steve Gutterman in Moscow, Christopher Torchia in Igoeti, Georgia; Dmitry Lovetsky in Ruisi, Georgia; and Paul Ames in Brussels, Belgium contributed to this report.