KIEV, Aug. 25 - The presidents of Ukraine and Russia will hold talks on Tuesday aimed at a possible settlement of the separatist war in Ukraine's east.

Since Vladimir Putin and Petro Poroshenko last met on June 6 in France, Ukraine has turned the tide of the conflict and largely encircled pro-Russian rebels holding out in two cities in the east of the former Soviet republic.

But the diplomatic crisis has only deepened, especially since the downing of a Malaysian airliner over rebel-held territory last month with the loss of 298 lives.

Ukraine accused Russia on Monday of sending soldiers across the border to open a new front, a charge that Moscow dismissed as the latest salvo in a campaign of misinformation, Reuters reported.

Poroshenko expressed "extraordinary concern" at the alleged move, his press service said.

Russia has consistently denied arming or fighting alongside the separatists. Stung by U.S. and EU sanctions against its finance, oil and defense sectors, it has hit back by banning most Western food imports, in a trade war that is hurting both the Russian and European economies.

With East-West tensions at their highest since the Cold War, Russian and NATO forces have both stepped up exercises in recent months.

Tuesday's talks, expected to begin after 0700 ET in the Belarussian capital of Minsk, will include European Union foreign policy chief Catherine Ashton and the leaders of Belarus and Kazakhstan, partners in a Russian-led customs union.

But expectations on all sides appear low, with German Chancellor Angela Merkel among those playing down any likelihood of a breakthrough to end the fighting, in which more than 2,000 people have been killed since April.

In the latest twist in a protracted conflict, the Ukrainian military said a group of Russian forces, disguised as rebels, had crossed into south-east Ukraine with 10 tanks and two armored infantry vehicles. It said border guards had halted the column outside Novoazovsk, Ukraine's most south-easterly point on the Azov Sea.

"This morning there was an attempt by the Russian military in the guise of Donbas fighters to open a new area of military confrontation in the southern Donetsk region," military spokesman Andriy Lysenko told journalists.

Lysenko later added that two tanks in the column had been destroyed and several members of "an intelligence-sabotage group" had been seized.

"The area is now blocked by Ukrainian troops," he said. (rt/ez)