* No apparent breakthrough in three-way meeting
* Russia repeats call for immediate ceasefire
* Polish FM says Ukraine NATO membership not on agenda (Adds quotes, context)
By Gabriela Baczynska
ST PETERSBURG, Russia, June 10 (Reuters) - Poland called on Russia on Tuesday to help defuse the crisis in Ukraine by preventing militants and weapons from crossing into the eastern part of the country, where pro-Russian rebels are fighting government forces.
Polish Foreign Minister Radoslaw Sikorski spoke at a joint news conference with his Russian and German counterparts after trilateral talks that failed to produce any breakthrough in a crisis that has badly strained Moscow's ties with the West.
"If Russia wants to prove that it wants de-escalation in Ukraine, the best way to do it would be to stop the flow of separatists and arms through the Russian-Ukrainian border," Sikorski said.
German Foreign Minister Frank-Walter Steinmeier took a more nuanced stance, saying both Russia and Ukraine needed to better control their common border and suggesting the need for "common border management in some form".
Russia's Sergei Lavrov repeated Moscow's demand that the Kiev government stop armed operations against the separatists, urging an immediate ceasefire and the start of talks on Ukraine's future.
"Ending the military operation against the protesters is of course key, in our view ... Nobody is interested in a continuation of war there," said Lavrov.
Tension between Lavrov and Sikorski was palpable during the news conference.
Sikorski said Ukraine, a sprawling former Soviet republic of 45 million people pitched between Russia and central Europe, had the right to deploy the army against armed groups on its soil.
Lavrov said that was a show of double standards, noting that the West had opposed the use of force by Ukrainian authorities against protesters who drove Moscow-backed president Viktor Yanukovich from power in February.
After Yanukovich's ouster, Russia annexed Ukraine's Crimea region in March and massed tens of thousands of troops near its long border with Ukraine, igniting fears in Kiev and the West that Moscow would seek to take over more Ukrainian territory.
Sikorski said he was glad to hear "that what Russia has done in Crimea will not be repeated" - a comment that drew ironic laughter from Lavrov who did not comment himself on that issue.
The Polish minister said Russian President Vladimir Putin's promise to respect the results of the May 25 presidential election that brought confectionary magnate Petro Poroshenko to power in Ukraine had been a step in the right direction.
Russia should not feel threatened by Poroshenko's plans for closer ties with the European Union, Sikorski said, adding that Ukrainian membership of NATO - something that Moscow strongly opposes - was "not on the agenda".
(Reporting by Gabriela Baczynska and Sabine Siebold; Writing by Steve Gutterman; Editing by Gareth Jones)