* U.S.-Taliban talks stymied by diplomatic row
* Kerry warns Taliban that office in Qatar could be closed
* U.S. envoy has arrived in Doha but U.S. awaiting Taliban move
By Lesley Wroughton and Yara Bayoumy
DOHA, June 22 (Reuters) - U.S. Secretary of State John Kerry put the onus on the Taliban to revive stalled efforts to end Afghanistan's 12-year-old war and warned the militants on Saturday they might lose their new office in Qatar if the peace bid collapsed.
U.S. officials were due to hold preliminary discussions with the Taliban in Qatar last Thursday - but they were called off after the Afghan government objected to the fanfare surrounding the militants' opening of an office in the Gulf state.
"We need to see if we can get back on track ... I don't know whether that's possible or not," Kerry told a news conference in Qatar.
"If there is not a decision ... to move forward by the Taliban in short order, then we may have to consider whether or not the office has to be closed."
Kerry did not spell out what steps he wanted the militants to take to revive the preliminary meeting, which had raised hopes that Washington might go on to broker the first direct negotiations between the Afghan government and the insurgents.
But Afghan government officials told Reuters they had been particularly angered by the Taliban's decoration of their building with a flag and plaques that suggested the group had achieved some level of international recognition.
The decorations had broken agreements on how the build-up to the talks would be handled, the government officials said.
The plaques bore the name of the "Political Office of the Islamic Emirate of Afghanistan", the name the Taliban used for the country when they controlled it.
The Taliban's flag was later lowered, but not removed. A name plate outside the office was taken down but a similar one inside was still in place.
U.S. ENVOY ARRIVED
Kerry said the U.S. special envoy for Afghanistan and Pakistan, James Dobbins, had arrived in Qatar for the talks, but added: "We are waiting to find out whether or not the Taliban will respond in order to follow the sequence, which has been very painstakingly established.
"We have performed our part in good faith. Regrettably, the agreement was not adhered to in the early hours," Kerry said.
U.S. officials had said the Taliban was expected to use the talks to seek the return of former commanders now held by Washington at the Guantanamo Bay military prison in Cuba.
The United States wants the return of the only known U.S. prisoner of war from the conflict, Sergeant Bowe Bergdahl, who is believed to be held by the Taliban.
Kerry on Saturday declined to comment on the prospect of Taliban prisoners being freed. "It's just not where the process is," he said.
The Taliban were pushed out of power in Afghanistan by the U.S. invasion that followed the al Qaeda attacks on U.S. targets on Sept. 11, 2001.
The group has since waged an insurgency to overthrow the government of Afghan President Hamid Karzai and oust foreign troops.
It has until now refused talks with Kabul, calling Karzai and his government puppets of the West. (Writing by Andrew Heavens; Editing by Kevin Liffey)
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