Russia has demanded the extradition of the London-based Chechen separatist leader Akhmed Zakayev after Polish police arrested him at a conference in Warsaw.

Zakayev – who was granted political asylum by Britain in 2003 – was detained early this on his way to see the Polish chief prosecutor. He arrived in Warsaw on Wednesday to attend the World Chechen Congress, a meeting of Chechen exiles.

Zakayev is the most high-profile surviving Chechen separatist leader from the 1990s, when he served as deputy prime minister in the quasi-independent government of Aslan Maskhadov.

The British court decision to grant asylum on the basis he might be tortured in Russia enraged the Kremlin, and contributed to a slump in UK-Russian relations.

Russia's prosecutor general, Yuri Chaika, phoned his Polish counterpart and passed on details of Zakayev's alleged involvement in terrorist activities. Russia had issued a warrant via Interpol for his arrest, and has been seeking his return for nearly a decade.

But Zakayev's friends said they were confident he would not be sent back to Russia, where he would face jail. "He is approaching it all with a large dose of calm," Adam Borowski, a conference organiser who was with him at the time of his arrest, told the Associated Press. "He says he believes Poland, as a democratic country, will not believe Russia's fabricated evidence. He believes Poland will not extradite him."

He was released last night by a Warsaw court, although Borowski said he will have to remain in the country pending a decision on his extradition. Since being granted asylum Zakayev has often travelled in Europe, visiting Poland three times this year, including three weeks ago. A London magistrates court struck out the original Russian arrest warrant in 2003. Up until now, EU states have accepted the London verdict.

"There is no reason to detain him. He should be able to rejoin the congress," Ivar Amundsen, director of the Chechnya Peace Forum, said. He blamed political pressure from Moscow for the arrest: "The congress shines a light on Russia's war crimes in the Caucasus. They [the Russians] don't like that," he told the Guardian.

Russo-Polish ties have improved after a plane crash in April that killed Poland's president Lech Kaczynski. Poland's prime minister, Donald Tusk, denied his government had acted on Kremlin orders.

Tusk told national radio a decision on Zakayev's extradition would be taken "in accordance with our understanding of Poland's interests, and with our sense of decency and justice. We will not be trying to meet anybody's expectations".

Last year Chechnya's Kremlin-installed president, Ramzan Kadyrov, tried to persuade Zakayev to return home, offering him a job as theatre director in the capital, Grozny. Zakayev, a former actor and the head of Chechnya's government-in-exile, held a series of discussions in Europe with Kadyrov's trusted aide Dukvakha Abdurakhmanov about political reconciliation. The plan fell through after Russia refused to drop outstanding terrorist charges against him. At the same time, Chechnya's current Islamist rebel leadership denounced Zakayev as a traitor and announced their intention to kill him.

Today Kadyrov said Zakayev should be handed back to Russia for trial, and then sentenced to life in prison.

Zakayev entered politics in 1994 as culture minister under Chechnya's first separatist president. He left Chechnya in 1999 after being wounded. His charisma has won him supporters including the actor Vanessa Redgrave, who has campaigned on his behalf and paid £62,600 bail after he was detained at Heathrow in 2002. He has said he represents the Chechen separatist political faction, and distanced himself from radical Islamist rebels.

This year he denounced the militant leader Doku Umarov who claimed responsibility for the Moscow subway bombings in March. Zakayev called the attack a "monstrous crime".

Chechen rebellion

The Chechen insurgency has evolved since the 1990s when Zakayev and other now-dead leaders sought to establish an independent state. The current generation of fighters are no longer battling for independence but want to establish a Taliban-style islamist emirate across Russia's northern caucasus.

The war has spilled over from Chechnya into the volatile neighbouring republics of Ingushetia and Dagestan, where bomb attacks and shootouts between rebels and government security forces recur on a daily basis. Last week a suicide bomber killed 17 people after blowing up a crowded market in Vladikavkaz, the predominantly Christian capital of North Ossetia.

The surviving separatist Chechen exiles from the 1990s have been dubbed "constitutionalists" to distinguish them from the radical Islamist "military resistance" which now dominates the insurgent hierarchy.

The most powerful people currently inside Chechnya, however, are the armed followers of Kadyrov, many of whom have been absorbed into the republic's security and military structures. Known as Kadyrovtsy and including many former rebels, they are accused of numerous human rights abuses.