NATO leaders have cautiously welcomed the ceasefire that was agreed last Friday afternoon between Ukraine, Russia, the separatist rebels, and the Council of Europe.

News of the agreement filtered through to the Celtic Manor Resort outside Newport, south Wales, as the NATO summit was winding up. Military and political leaders were quick to express their scepticism about the deal.

"We look at actions fairly carefully. We have had quite a lot of words. Some of those words have proven not to be worth terribly much," the Deputy Supreme Allied Commander in Europe, General Sir Adrian Bradshaw, said. "There has been some deception, and some deceit. Right now, I can't tell you that there is any substantial change to the reality on the ground; and the reality on the ground is that Russian regular armed forces are being employed on the territory of Ukraine in support of this separatist movement."

The Prime Minister told a press conference that the increased sanctions against Russia that had been agreed earlier by the European Council would go ahead. "The announcement about the ceasefire is good news," Mr Cameron said. "I think we need to look carefully at whether it is a ceasefire, or whether it also includes a commitment, as I understand it might, to make real progress on a proper peace plan. . .

"If the ceasefire and a proper peace plan are put in place, then, of course, it would be right to look and see how those sanctions could potentially be removed, if proper milestones were reached."

President Obama said: "We are hopeful, but also - based on past experience - sceptical that the separatists will follow through, and that the Russians will stop violating Ukraine's sovereignty and territorial integrity. It has to be tested."

Earlier, NATO leaders had agreed a "comprehensive and tailored package" of measures to support Ukraine, focusing on cyber defence, logistics, and command and control communications, as well as on rehabilitation for troops injured in the conflict. NATO will also provide advice on defence reforms, as well as financial support of 15 million for defence-capacity building training.

Announcing the package, the outgoing secretary-general of NATO, Anders Fogh Rasmussen - who will be replaced at the end of this month by Jens Stoltenberg - emphasised that the military alliance was seeking a political and diplomatic solution to the crisis in Ukraine. He said that "nobody wants war."

"Ukraine has been an important and distinctive NATO partner for many years," Mr Rasmussen said. "We highly value Ukraine's contribution to our operations and the NATO response force. Ukraine has stood by NATO. Now, in these difficult times, NATO stands with Ukraine.

"We stand united in our support of Ukraine's sovereignty, and of territorial integrity within its internationally recognised borders. We strongly condemn Russia's repeated violations of international law. Russia must stop its aggressive actions against Ukraine, withdraw its thousands of troops from Ukraine and the border regions, and stop supporting the separatists in Ukraine."

Mr Rasmussen made his comments at a press conference at the NATO summit, alongside the Ukrainian President, Petro Poroshenko. Six months ago, Mr Poroshenko was the head of a confectionery company. Today he is the leader of a country at war, who last week was pleading for assistance at the top table of the world's largest military alliance. He said Ukraine was fighting for peace, not for war.