By Jeff Mason and Ece Toksabay
ANKARA (Reuters) - U.S. Vice President Joe Biden sought on Wednesday to ease tensions with Turkey over its demands for extradition of a cleric it blames for July's failed coup, saying Washington was cooperating but needed evidence to meet U.S. legal standards.
Demands for the extradition of Fethullah Gulen, in exile since 1999, and Turkish perceptions of an unsympathetic Western response to the coup soured relations between the United States and Turkey, a NATO partner in the U.S.-led war on Islamic State.
President Tayyip Erdogan had said Washington had "no excuse" for keeping hold of Gulen, a former Erdogan ally who Turkish officials say has operated a network of followers inside the armed forces and civil service to take over Turkey.
Speaking after meeting Erdogan in Ankara, Biden said those involved in the coup attempt were terrorists and said the U.S. had more lawyers working on the Gulen extradition request than in any other such recent case.
"We will abide by our system. We will continue to abide by the system and, God willing, there will be enough data and evidence to be able to meet the criteria that you all believe exist," Biden said. "We have no reason to shelter someone who would attack an ally and try to overthrow a democracy."
Erdogan blames Gulen for masterminding the coup by rogue troops that killed 241 people. Gulen has denied any involvement and condemned the military rebellion during which soldiers commandeered tanks and jets to attack government buildings.
"For us the priority is the extradition of Gulen as soon as possible," Erodogan said in a joint press conference with Biden. "But the agreement between the United States and Turkey requires the detention of such people. This individual continues to manage a terrorist organization from where he is."
Lawyers say the process could take years. Even if approved by a judge, an extradition request would still have to go to the U.S. Secretary of State, who can consider non-legal factors, such as humanitarian arguments.
After meeting Biden, Prime Minister Binali Yildirim said Turkey and the United States should never allow incidents to harm relations, but Ankara expected the legal process for the Gulen extradition without delay.
"If the extradition process of this terrorist leader could accelerate, if our cooperation on this matter continues like this, the Turkish people will quickly recover from their sadness and disappointment," the premier said.
The government has cracked down on suspected Gulen followers, detaining more than 40,000 people and formally arresting about half of them. About 80,000 people in the judiciary, police, civil service and elsewhere have been sacked or suspended.
Turkish authorities fired more than 2,800 judges and prosecutors on Wednesday, in the latest purge related to the coup, broadcaster CNN Turk reported.
Critics fear Erdogan is using the coup as a pretext to curtail dissent. Biden, who made strong statements on free speech and free expression on his last visit to Turkey, was less vocal this time.
Biden said that the prime minister, the foreign minister and others had made it clear they would adhere to constitutional principles and that the rule of law would prevail.
"Let's give them some time. I believe they mean what they say. And so let's move on," said Biden.
Turkish officials gave Biden a guided tour around the parliament, which was bombed during the coup attempt.
Ankara will probably send the United States a coup-related extradition request for Gulen next week, the Turkish justice minister said on Wednesday.
Washington has said it needs clear evidence to extradite Gulen. The U.S. State Department said this week that documents submitted so far by Ankara constituted a formal extradition request, although not on issues related to the coup.
(Additional reporting by Ayla Jean Yackley; Writing by Patrick Markey; Editing by David Dolan and Louise Ireland)