Kiev (AFP) - Ukraine on Monday banned the transit of Russian trucks across its territory in a tit-for-tat response to an escalating trade war between the feuding ex-Soviet states.

The measure follows a halt to all flights between the neighbours and an effective Russian freeze on Ukrainian imports that have hit the cash-strapped country's industrial exports especially hard.

It also underscores the vast amount of energy Kiev's Western allies must still spend to resolve Ukraine's 21-month eastern separatist conflict and to mend their own tattered relations with Moscow.

The Ukrainian government said its decision was taken because Russia had "violated the World Trade Organization's rules and procedures and bilateral intergovernmental agreements... by unilaterally halting the movement of Ukrainian trucks."

It added that the ban would stay in force until Kiev received an adequate explanation from Moscow.

Russia's transport ministry said on Sunday it was imposing its restrictions "in response to the suspension of passage" of its own trucks across Ukraine.

Nationalist groups in western Ukraine had spent nearly a week trying to keep Russian trucks from crossing into the rest of Europe in protest over the Kremlin's alleged support for pro-Russian separatists in the country's east.

But no formal decision to stop Russian traffic had been taken by the Ukrainian government itself before Monday's statement.

Moscow's response to Kiev's announcement was swift.

"This is an issue of tremendous importance," Russian news agency quoted Kremlin spokesman Dmitry Peskov as saying in Moscow.

"It absolutely outrageous to see such travesties against our truckers being tolerated by the Ukrainian authorities."

And Prime Minister Dmitry Medvedev called the situation "disgraceful".

"This has to be given an adequate response," Medvedev told his cabinet.

Moscow news reports said Medvedev suggested shutting the Russian border to all forms of traffic coming in from Ukraine.

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- Munich failure -

Germany and France have been spearheading Western efforts to find a mutually acceptable solution that could end Ukraine's separatist conflict and warm Kiev's frozen ties with Moscow.

The pro-Russian insurgency that Moscow denies backing has killed more than 9,000 people and left the rebels in control of a region roughly the size and population of Wales.

The revolt was fuelled by the February 2014 ouster of Ukraine's Russian-backed president and Moscow's seizure of Crimea the following month.

But efforts by Paris and Berlin to bridge some ground between Moscow in Kiev during last week's Munich Security Conference fell flat.

German Foreign Minister Frank-Walter Steinmeier emerged from Saturday's meeting to warn that time was running out for the two sides to settle their disputes.

The West has imposed tough economic sanctions on Russia that Moscow has countered by banning imports of food from nations allied with the new Ukrainian leadership.

Several EU state hit especially hard by Russia's trade embargo have been hoping to ease some of the bloc's punitive measures against Moscow when they come up for a review in July.

But US Secretary of State John Kerry said on Saturday that sanctions against Russia would remain in place until Moscow implemented all aspects of a peace plan agreed by the sides one year ago.

"Put plainly, Russia can prove by its actions that it will respect Ukraine’s sovereignty, just as it insists on respect for its own," Kerry said.