KIEV, June 8 - Ukraine's defense minister on Monday accused pro-Russian rebels backed up by Moscow's forces of assembling a 40,000-strong army sufficient for a "mid-sized European state,” AFP reported.

Stepan Poltorak's estimates fly in the face of Russia's denials that it either backs the separatist fighters or covertly sneaks troops across its southwestern border into the Ukrainian war zone.

President Petro Poroshenko last week put the number of active Russian soldiers in his former Soviet republic's industrial east at more than 9,000.

But Russian President Vladimir Putin describes Russians fighting against Ukraine's pro-Western government troops as patriotic volunteers and off-duty soldiers who are answering "a call of the heart."

Moscow has also distanced itself from two Russians captured last month who have told Ukrainian interrogators and Western reporters that they were active members of the Kremlin's special military reconnaissance force.

The Ukrainian defense minister said the insurgent army -- in control of parts of the Russian-speaking Luhansk and Donetsk regions that are home to about four million people -- could muster more than 550 tanks and an arsenal of other heavy weapons.

"The combined size of the Russian armed forces and illegal armed formations... stands at more than 42,500," Poltorak told a group of visiting lawmakers from NATO countries.

"This amount of weapons, as we all understand, would be sufficient for a mid-sized European state."

Poroshenko said Kiev's own eastern force had grown to more than 50,000 after being limited to 5,000 soldiers at the onset of the war 14 months ago.

Ukraine's latest charges come against the backdrop of growing fears that the ceasefire that Germany and France helped forge in February is now falling apart.

Clashes around the 10,000-strong town of Marinka -- straddling the twisting line separating Kiev's forces from the militants -- and other disputed villages claimed some 30 lives last week and threatened to escalate on Monday.

"Our positions near Marinka came under small weapons and mortar fire this morning," Ukrainian military spokesman Andriy Lysenko told AFP by telephone.

A rebel defense spokesman denied the charges and called the situation around the heavily-damaged town "calm.” (afp/ez)