KHARKIV, Feb. 22 – Ukraine said on Sunday it feared unrest could spread beyond territory held by pro-Russian separatists, after an explosion killed two people at a memorial rally in an eastern city far from the front line, Reuters reported.

Kiev said it arrested four people who had been armed and trained in Russia after the blast, which killed a policeman and a demonstrator at the rally in Kharkiv, the biggest city in the east, 125 miles from the war zone.

A week after a ceasefire agreement that Moscow-backed rebels ignored to capture a strategic town, Kiev and its Western allies are trying to determine whether the separatists will now halt, or advance deeper into territory the Kremlin calls "New Russia."

Germany and France mediated the peace deal that came into effect a week ago, and say they still hope it can be resurrected, even though the rebels ignored it to inflict one of the worst defeats of the war, seizing the town of Debaltseve after encircling thousands of Ukrainian troops.

In signs that there may be at least a pause now that the rebels achieved that objective, government and separatist forces exchanged prisoners overnight. The rebels said on Sunday they would begin withdrawing artillery from the front.

But Kiev said Moscow was moving more troops and armor into eastern Ukraine near a port it fears is the next target. Russia denies it has troops in eastern Ukraine.

Ukrainians held marches and memorial services on Sunday for 100 people killed a year ago during an uprising that toppled a pro-Russian president and led to the war in which more than 5,500 people have since been killed.

At the rally in Kharkiv, amateur footage posted on the Internet showed a few hundred marchers with Ukrainian flags, who shouted "glory to the heroes!" just before being hit by an explosion. Demonstrators and bystanders, including a woman pushing a baby in a pram, fled in panic.
A wounded man in military uniform lay in the snow shouting for help.

"Today is memorial Sunday, but on this day terrorist scum revealed its predatory nature," President Petro Poroshenko said on Facebook. "This is a brazen attempt to expand the territory of terrorism."

Kiev has long worried that Russia aims to foment instability far beyond regions now held by separatists.
Kharkiv, with 1.4 million people, has occasionally seen violent protests by separatists in the past year but is firmly under Kiev's control.

Markian Lubkivskyi, an aide to the head of Ukraine's SBU security service, said four arrested suspects planned a series of attacks in the city with a Russian "Shmel" rocket launcher.

"They are Ukrainian citizens, who underwent instruction and received weapons in the Russian Federation, in Belgorod," he told Ukraine's 112 Television. Belgorod is a city across the nearby Russian border from Kharkiv.
Moscow did not immediately respond to the accusations. It has long denied aiding its militant sympathizers in Ukraine.

Ukraine's most immediate fear is of an attack on the port of Mariupol near the front, with 500,000 people the biggest government-held city in the two rebellious provinces.

The Ukrainian military said the rebels were pressing on with attacks on government forces nearby, and Moscow was reinforcing.

Spokesman Andriy Lysenko said a military train carrying 60 armored vehicles including tanks had arrived in the town of Amvrosiivka from Russia on Saturday. A convoy of military equipment had later crossed the border near Novoazovsk, east of Mariupol on the Sea of Azov.
He said fighting was in progress at the village of Shyrokyne, east of Mariupol.

"Our soldiers are holding their positions," Lysenko said, adding that there had been a total of 44 attacks by separatists across the conflict zone in the past 24 hours.

Reuters journalists saw a 20-vehicle convoy of separatist military trucks with anti-aircraft missile systems and howitzers heading west from the recently-captured town of Debaltseve. (rt/ez)