(Reuters) - Kiev accused Russia on Friday of sending more tanks and troops into eastern Ukraine and said they were heading towards the rebel-held town of Novoazovsk on the southern coast, expanding their presence on what could be the next battlefront.

Russia did not immediately respond to the accusation which, if confirmed, would help kill off a European-brokered truce that was met by relentless rebel advances since it came into force on Sunday. Moscow has always denied charges in the past that its forces are fighting in Ukraine.

Novoazovsk lies on the Sea of Azov, 25 miles east of the port city of Mariupol. It was captured by rebels last year and Kiev fears it could be a launch pad for strikes on Mariupol, a government-held port of 500,000 people that controls routes to the south and possibly to the Crimea peninsula annexed by Russia a year ago.

"In recent days, despite the Minsk (ceasefire) agreement, military equipment and ammunition have been sighted crossing from Russia into Ukraine," military spokesman Andriy Lysenko said. He said more than 20 Russian tanks, 10 missile systems and busloads of troops had crossed the border into Ukraine. The United States also says it has sighted Russian reinforcements.

Kiev said rebels had attacked 49 times in the last 24 hours, proof that they were still ignoring the truce, despite having achieved their main objective this week by capturing the railway hub of Debaltseve. The rebels said government forces also fired.

Western nations have publicly clung to the hope that they can revive the peace deal brokered by France and Germany in the Belarussian capital Minsk on Feb. 12, even though the rebels ignored it to seize Debaltseve, inflicting one of the worst defeats on Kiev of the 10-month-old war.

"We are more convinced than ever that they must be applied - all the agreements, nothing but the agreements," French President Francois Hollande said in Paris alongside German Chancellor Angela Merkel on Friday.

'THESE ARE OURS NOW'

In Debaltseve, where Kiev was forced to withdraw thousands of besieged troops this week, the black, blue and red flag of the rebels' self-proclaimed Donetsk People's Republic flew over the town hall. Artillery could be heard in the distance.

Walls were pock-marked by bullets or had huge holes blown in them. Burnt-out hulks of tanks and military trucks lay abandoned on the road. Heavily armed rebels and tanks patrolled the streets on the outskirts, where bridges had been blown up and the railway appeared to have suffered major damage.

A separatist fighter picked out ammunition left by fleeing government troops from the rubble.

"These are ours now, and we'll use them against them. We have to expand," said the rebel who refused to give his own name, straightening up while a dozen others continued their search for arms and ammunition.

The town held around 27,000 people before the fighting. Most fled during the battle, but thousands remained trapped inside, sheltering in cellars during days of relentless bombardment. Several hundred lined up for food in the center of town. Many were weeping as they stood in the queue.

"We're waiting. They should bring dry meals in blue packaging since the pasta is already finishing," said Yulia, 28, a teacher, holding her 10-year- old niece by the hand.

DARK MOOD AT UPRISING ANNIVERSARY

In the capital Kiev, the military setbacks darkened the mood as crowds gathered for the first anniversary of the uprising that toppled the Moscow-leaning president Viktor Yanukovich but culminated in war.

Ukraine's President Petro Poroshenko accused a top aide to Russia's Vladimir Putin of being behind the sniper killings of 100 Ukrainian protesters on the streets of Kiev during the uprising a year ago.

"Just a few days ago, the head of state security told me that special forces operatives gave evidence that the Russian presidential aide Vladislav Surkov led the organization of groups of foreign snipers on the Maidan," Poroshenko told some of the relatives of those killed, according to his website.

Russia's Foreign Ministry called the accusation "madness".

Crowds headed to observe the anniversary at Independence Square in the heart of the capital, known locally as "the Maidan" and revered by Ukrainians as platform of a revolution that turned the country away from Russia and towards Europe.

"We have shown the world, we have shown everyone that we can stand against the regime without weapons, that we are free people and we will fight till the end, till victory," said Mykola Tokar who traveled from Lviv region in the west to attend Maidan ceremonies in Kiev.

Some people wore combat fatigues showing allegiance to pro-government militias that have alongside Kiev's troops against pro-Russian separatists. The mood was somber.

More than 5,600 people have been killed in fighting since mid-April last year, soon after Russia annexed Crimea from Ukraine following Yanukovich's overthrow.

(Additional reporting by Natalya Zinets; Writing by Timothy Heritage and Richard Balmforth; Editing by Peter Graff)