* Five-day pause in Turkish offensive expires at 1900 GMT
* Erdogan flies to Russia to discuss Syria with Putin
* Says Kurdish YPG militia continuing to withdraw in NE Syria
* Says Turkey to resume offensive if US does not honour promise
By Darya Korsunskaya and Humeyra Pamuk
SOCHI, Russia/WASHINGTON, Oct 22 (Reuters) - The commander of Kurdish forces in northeast Syria told the United States he had met all obligations set out in a U.S.-brokered truce, a senior U.S. official said on Tuesday, as Washington warned it would punish Turkey if it resumes hostilities.
The five-day truce in Turkey's cross-border offensive to allow the withdrawal of Kurdish YPG fighters from the border area ends at 10 pm (1900 GMT) on Tuesday, and President Tayyip Erdogan has said Turkey could then press on with fighting.
Earlier on Tuesday, as he flew to Russia for talks on Syria, Erdogan said hundreds of Kurdish fighters remained near to Syria's northeast border despite the truce demanding their withdrawal.
Erdogan said up 800 fighters from the Kurdish YPG militia had left the area near the border, where Turkey plans to establish a "safe zone" extending more than 30 km (20 miles) into Syria, but 1,200 to 1,300 of them remained.
However, the senior U.S. administration official said Ankara and Washington were in contact to agree that the withdrawal has taken place, and that Turkey's pause in its military offensive into Syria would turn into a permanent halt of the campaign.
Erdogan held talks on Tuesday with President Vladimir Putin of Russia, the other main international power in Syria, in the Black Sea resort of Sochi.
Turkey began its cross-border operation nearly two weeks ago following U.S. President Donald Trump's decision to withdraw American troops from northern Syria.
The American withdrawal from Syria has been criticized by U.S. lawmakers, including some of Trump's fellow Republicans, as a betrayal of Kurdish allies who have helped the United States fight Islamic State in Syria.
Trump said on Monday it appeared that the five-day pause was holding despite skirmishes, and that it could possibly go beyond Tuesday's expiry, but Erdogan said the fighting may resume.
"If the promises given to us by America are not kept, we will continue our operation from where it left off, this time with a much bigger determination," he said.
Turkey says it wants to set up a "safe zone" along 440 km (275 miles) of border with northeast Syria, but its assault so far has focused on two border towns in the centre of that strip, Ras al Ain and Tel Abyad, about 120 km apart.
A Turkish security source said initially the YPG was pulling back from that 120 km border strip. He said Erdogan and Putin would discuss a wider withdrawal from the rest of the border in their talks on Tuesday in the Russian Black Sea resort of Sochi.
Syrian and Russian forces have already entered two border cities, Manbij and Kobani, which lie within Turkey's planned "safe zone" but to the west of Turkey's military operations.
Erdogan has said he could accept the presence of Syrian troops in those areas, as long as the YPG are pushed out.
"My hope is that God willing we will achieve the agreement we desire," he said before leaving for Sochi.
The Kremlin said it hoped Erdogan would be able to provide Putin with more information about Ankara's plans for northeast Syria, and was also studying what it described as a new idea from Germany for an internationally controlled security zone in northern Syria involving Turkey and Russia.
German Defence Minister Annegret Kramp-Karrenbauer said the step should stabilise the region so that civilians could rebuild and refugees could return on a voluntary basis.
Russia is a close ally of Syrian President Bashar al-Assad. Turkey has backed rebels seeking to oust Assad during Syria's more than eight-year-long civil war but has dropped its once-frequent calls for Assad to quit.
Ankara is holding covert contacts with Damascus, partly via Russia, to avert direct conflict in northeast Syria, Turkish officials say, although publicly hostility between the two governments remains.
"Erdogan is a thief and is now stealing our land," Assad said during a rare visit to a separate frontline in Syria's northwestern Idlib region, the last major bastion of Turkey-backed rebels.
Some 300,000 people have been displaced by Turkey's offensive and 120 civilians have been killed, according to the Syrian Observatory for Human Rights, a UK-based war monitor. It said on Sunday 259 fighters with the Kurdish-led forces had been killed, and 196 Turkey-backed Syrian rebels. Turkey says 765 terrorists but no civilians have been killed in its offensive.
The U.S. withdrawal has left a vacuum into which Turkish forces have pressed in from the north, while from the southwest Russian-backed Syrian troops have swept back into territory they were driven from years ago.
(Additional reporting by Ali Kucukgocmen and Ezgi Erkoyun in Istanbul, Ahmed Rashid in Baghdad and Andrei Kuzmin in Moscow Writing by Dominic Evans Editing by Gareth Jones)
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