Ukraine’s president, Petro Poroshenko, has sought to forge a united front with Germany and France against a Russia that he said was still threatening to invade his country and was arming separatist forces.

Before flying to Berlin to meet German chancellor Angela Merkel and French president François Hollande tonight, Mr Poroshenko said the three leaders “must co-ordinate their positions and approaches” ahead of possible talks next month that would include Russian president Vladimir Putin.

“We must ensure that Russia respects the Minsk agreements,” Mr Poroshenko said, referring to a ceasefire agreed in February that reduced but did not stop violence in eastern Ukraine, where almost 7,000 people have been killed and some 1½ million displaced during 16 months of fighting.

Dr Merkel’s spokesman, Steffen Seibert, noted that “in recent weeks, the security situation in eastern Ukraine has worsened, which leads not only to grave difficulties for the population, but also for the [international] observer mission.”

In the last 10 days, deaths and injuries among civilians and soldiers have increased in several disputed areas, amid intensified exchanges of artillery fire from heavy weapons that are supposed to have been withdrawn under the Minsk deal.

Addressing crowds in Kiev during celebrations for Ukraine’s Independence Day, Mr Poroshenko accused Russia of sending three large convoys of weapons to the separatists this week.

During the whole conflict, Mr Poroshenko claimed, Russia had sent hundreds of tanks and artillery systems to the rebels, and stiffened their 40,000-strong force with about 9,000 Russian soldiers.

Some 50,000 Russian troops were now deployed close to Ukraine’s borders, he added, warning that the threat of “full-scale military invasion” remained.

“We stand for peace, but we are not pacifists,” Mr Poroshenko said, after a military parade to mark 24 years since Ukraine broke from the Soviet Union.

“We must get through the 25th year of independence as if on thin ice. We must understand that the smallest misstep could be fatal,” he said.

“The war for independence continues, and we can only claim victory by combining our defensive efforts, diplomatic talent, political responsibility and steely determination.”

With the Minsk agreements fraying and diplomacy at a near-standstill, Kiev and Moscow accuse each other of preparing for an escalation in hostilities: Russia now has thousands of troops on exercises near Ukraine’s border, and Ukraine is sending more armoured vehicles to reinforce positions in the east.

Mr Poroshenko said that if Russia did not commit itself to peace “the reaction of the international community should be immediate and resolute – these are the messages I will take to my talks in Berlin.”

Russian foreign minister Sergei Lavrov called Mr Poroshenko’s comments “unfounded and disgraceful”.

“Their goal is to break the ‘genetic code’ ensuring the unity of our nations. I think he won’t succeed in that,” he said of Russians and Ukrainians.

Mr Lavrov also said Russia would welcome a chance to improve relations with Washington, and detected faint “signals” that the United States may be considering this.