Britain believes that nearly 180 Russian battle tanks or armoured personnel carriers are deployed with Ukrainian separatists in the east of the country, supported by more than 1,000 regular Russian troops.

Government sources have accused Moscow of "completely disregarding the sovereignty and territorial integrity of a neighbour" after an intelligence estimate of the weaponry in Ukraine and of direct shelling of Kiev's forces from Russia.

The estimate of Russian weaponry was outlined by Sir Mark Lyall Grant, the British ambassador to the UN, who told the security council that Moscow had sent:

• 1,000 regular Russian troops

• Up to 100 main battle tanks

• 80 armoured personnel carriers

• 100 shoulder-launched missile weapons

• 500 anti-tank weapons

• More than 100 artillery pieces

A government source said: "We are clear that formed units of the Russian armed forces are now directly engaged in fighting inside Ukraine. We believe that the units consist of well over 1,000 regular Russian troops equipped with armoured vehicles, artillery and air defence systems.

"We think that there are over 1,000 Russian troops fighting as part of the pro-Russian separatists in eastern Ukraine. This is the arsenal we assess the separatists have. We also believe that Russia has shelled Ukrainian territory.

"In just over five days, from 14-19 August, we think Ukrainian armed forces were fired on from positions inside Russian territory on at least 21 separate occasions. This is further provocative action by Russia completely disregarding the sovereignty and territorial integrity of a neighbour."

David Cameron will use the figures to urge fellow EU leaders at a summit in Brussels on Saturday to toughen sanctions against Russia.