Polish Prime Minister Donald Tusk held talks with Russian leaders on a one-day visit designed to ease tensions over energy, trade and US plans to station elements of its missile defence shield on Polish soil.
A Polish reporter covering Tusk's visit was briefly detained by Russian officials before rejoining the Polish delegation after Russian premier Viktor Zubkov intervened.
Reporter Waclaw Radziwinowicz, who works for Polish newspaper Gazeta Wyborcza, said he believed the incident was "political punishment" for his reporting on Russia and its ex-Soviet neighbours.
Ties between Poland and its former Warsaw Pact overlord have been all but frozen for the past two years but signs of a thaw emerged when Tusk replaced Jaroslaw Kaczynski late last year.
Zubkov described Tusk's visit as "an important step in Russian-Polish relations" in opening remarks at their meeting. Tusk responded: "I'm glad we have found a common language."
Later, in the highest-level talks between the two countries since 2004, Tusk will meet Russian President Vladimir Putin and his likely successor Dmitry Medvedev.
Last year, the previous Polish government blocked EU-Russia strategic partnership talks in response to a Russian ban on imports of Polish meat.
In the past few months Russia has partially lifted the meat embargo and a senior Kremlin aide said on Thursday he was hopeful the veto on EU-Russian talks would be lifted soon.
Moscow is also unhappy about talks between Poland and the United States on hosting elements of the planned U.S. missile defence shield on Polish soil. Russia says the shield is a threat to its own national security.
A Russian plan to build a gas pipeline under the Baltic Sea to Germany, bypassing Poland, is another irritant. Tusk is seeking to persuade the Kremlin to drop the plan and build an overland link through Poland instead.
Radziwinowicz was detained by officials as he entered the White House government headquarters to report on the Zubkov-Tusk talks. He was placed in a minibus and told he would be taken to the airport, a spokesman for Tusk said.
The reporter rejoined the press corps after representations from the Polish delegation. Zubkov had given assurances he would be allowed to cover the visit, the spokesman said.
Radziwinowicz said he had been a Moscow-based reporter and had been deported from Belarus, a close Russian ally which has tetchy relations with neighbouring Poland.
"What has happened today looks like a pure provocation to me, especially because they gave me a visa yesterday," he said. "It's political punishment."
