WRAPUP 10-Russia gives up key northeast towns as Ukrainian forces advance

(Adds background, Ukraine foreign minister asking for more weapons, pro-Russian separatist, Luhansk governor)

* Russia's worst setback since Kyiv push abandoned in March

* Ukraine capture of railway hub cuts supplies

* Could be a decisive turning point in six-month war

* Russia says troops sent to reinforce operations in Donetsk

By Max Hunder and Vitalii Hnidyi

KYIV/HRAKOVE, Ukraine, Sept 10 (Reuters) - Moscow abandoned its main bastion in northeastern Ukraine on Saturday, in a sudden collapse of one of the war's principal front lines after Ukrainian forces made a rapid advance.

The swift fall of Izium in Kharkiv province was Moscow's worst defeat since its troops were forced back from the capital Kyiv in March. Ukraine hailed it as a turning point in the 6-month-old war, with thousands of Russian soldiers leaving behind ammunition stockpiles and equipment as they fled.

Russian forces used Izium as the logistics base for one of their main campaigns - a months-long assault from the north on the adjacent Donbas region comprised of Donetsk and Luhansk.

The state-run TASS news agency quoted Russia's defence ministry as saying it had ordered troops to leave the vicinity and reinforce operations elsewhere in Donetsk.

The head of Russia's administration in Kharkiv told residents to evacuate the province and flee to Russia to "save lives," TASS reported. Witnesses described traffic jams of cars with people leaving Russian-held territory.

If the reported gains are held, it would be a serious blow for Russia, which Western intelligence services say has suffered huge casualties. It would also be a big boost for Ukraine, which is keen to show Western nations supplying it with weapons it deserves their continued support.

There is pressure on Kyiv to demonstrate progress before winter sets in, amid threats by Russian President Vladimir Putin to halt all energy shipments to Europe if Brussels goes ahead with a proposal to cap the price of Russian oil exports.

Ukraine's Foreign Minister Dmytro Kuleba said in Kyiv that Ukrainian forces had demonstrated they were capable of defeating the Russian army with the weapons given to them.

"And so I reiterate: the more weapons we receive, the faster we will win, and the faster this war will end," he said.

In his nightly video address on Saturday, President Volodymyr Zelenskiy said Ukraine's armed forces had recovered around 2,000 square kilometres (770 square miles) of territory since its counter-offensive was launched earlier this month.

"The Russian army is claiming the title of fastest army in the world ... keep running!" Andriy Yermak, Zelenskiy's chief of staff, wrote on Twitter.