Russia has offered Iran advanced surface-to-air missiles after scrapping a similar deal in 2010 because of U.N. sanctions over Tehran's nuclear program, the state defense company said Monday.

Any such a deal is likely to go down badly in Washington as Western countries seek to keep up the pressure on Iran to agree a comprehensive deal on its nuclear activities.

Ukraine's military said Monday that it is waiting for a full ceasefire with pro-Russian rebels before withdrawing heavy weapons from the frontline, a key next step in a tattered peace plan.

"As Ukrainian positions are still being fired upon there can be no talk yet of a withdrawal of weapons," military spokesman Vladyslav Selevnyov wrote in a statement on Facebook. 

Soviet-era music, remixed to a modern techno track, thunders across Lenin Square in Debaltseve, where a woman jigs a couple of steps in dance.

Behind her, hundreds of residents of the town, shattered after months of fighting between pro-Russian rebels and the Ukrainian army, line up to receive a cardboard box of food and other emergency supplies provided by the Red Cross.

Germany's foreign minister warned Sunday in comments to a newspaper that any attack on the eastern Ukrainian city of Mariupol would be a clear violation of a week-old ceasefire accord.

Asked by Germany's Bild newspaper where, for him, the red lines in the Ukraine conflict lay, Frank-Walter Steinmeier said they had been drawn in the Minsk ceasefire deal that Germany helped broker.

With a sliver of moon barely illuminating the frostbitten east Ukrainian countryside, two patrols converged on foot, in the middle of a road strewn on either side with mines.

The government soldiers had arrived by bus from rebel strongholds at sundown Saturday, with those brought from Donetsk in civilian clothing while their comrades held in Lugansk sported fatigues.

A senior British minister ruled out sending arms to Ukraine Sunday as the United States and European nations sought ways to pressure Russia over the conflict in the ex-Soviet republic's east.

William Hague, who was foreign secretary until last year and is still a minister seen as close to Prime Minister David Cameron, said governments should think "very, very carefully" about such a move.

Ukraine's army and separatist rebels appeared Sunday to be complying at least partially with their truce accord, saying they will start pulling back heavy weapons from the frontline after carrying out a prisoner exchange.

But ongoing breaches of a week-old ceasefire -- especially by the pro-Russian rebels, who overran a strategic town in a bloody offensive -- have already prompted a threat from the United States of "serious" new sanctions against Moscow within days.

Thousands of pro-Kremlin activists took to the streets of central Moscow on Saturday vowing to prevent a Ukraine-style uprising in Russia.

The rally by the Anti-Maidan movement marked one year since scores of demonstrators were gunned down in Ukraine's pro-Western uprising that came to be known as the Maidan protests.

Ukraine lost 179 troops in a month-long battle with pro-Russian rebels that ended in defeat over the key eastern town of Debaltseve, an advisor to the country's president said.

If the figure is confirmed, it would represent one of the bloodiest losses suffered by the Ukrainian side in the 10-month conflict. 

Pro-Russian rebels said they will swap prisoners with the Ukrainian side Saturday as part of a battered truce that the West hopes will cool a deadly conflict that has poisoned relations with Moscow.

"Today (Saturday) there will be an exchange between us and the Ukrainian side," said the rebels' official for human rights, Daria Morozova.