Russian forces are engaged in direct military operations inside Ukraine in a blatant violation of Ukraine's sovereignty and territorial integrity, Nato secretary-general Anders Fogh Rasmussen said today.
He also said Nato would fully respect any decision by the Ukrainian parliament to put the country on a path to joining the US-led Western military alliance.
Ukrainian prime minister Arseny Yatseniuk said earlier his government would ask parliament to abandon Ukraine’s non-aligned status and set the country on a course to seek to become a member of Nato.
“Despite Moscow’s hollow denials, it is now clear that Russian troops and equipment have illegally crossed the border into eastern and south-eastern Ukraine,” Mr Rasmussen told reporters after Nato ambassadors held an emergency meeting with their Ukrainian counterpart at Kiev’s request.
“This is not an isolated action, but part of a dangerous pattern over many months to destabilise Ukraine as a sovereign nation,” he added.
"Russian forces are engaged in direct military operations inside Ukraine...Russia continues to maintain thousands of combat-ready troops close to Ukraine's borders. This is a blatant violation of Ukraine's sovereignty and territorial integrity. It defies all diplomatic efforts for a peaceful solution," he said.
The United States openly accused Russia of sending combat forces into Ukraine and threatened to tighten economic sanctions, but Washington stopped short of calling Moscow's intensified support for separatist forces an invasion.
President Barack Obama again ruled out US military action, saying there must be a diplomatic solution.
But he said he would reaffirm US commitment to Nato allies in the region at a summit next week.
"We are not taking military action to solve the Ukrainian problem. What we're doing is to mobilise the international community to apply pressure on Russia," he told reporters at the White House.
After days in which pictures appeared of Russian soldiers in uniform and Russian weapons in action in a renewed offensive against Ukrainian troops, Washington brushed aside Moscow’s disavowals of direct involvement in the fighting.
"Russia has ... stepped up its presence in eastern Ukraine and intervened directly with combat forces, armored vehicles, artillery, and surface-to-air systems, and is actively fighting Ukrainian forces as well as playing a direct supporting role to the separatists' proxies and mercenaries," State Department spokeswoman Jen Psaki told a media briefing.
“We have a range of tools at our disposal” to respond, she said, and added that increased sanctions on Russia were “the most effective tool, the best tool.”
A total of 2,593 people, including civilians as well as Ukrainian and separatist combatants, have been killed in fighting in eastern
Ukraine since it erupted in mid-April, a senior UN human rights official said today“The trend is clear and alarming. There is a significant increase in the death toll in the east,” Ivan Simonovic, UN assistant secretary general for Human Rights, told journalists.
“The current number of killed is 2,593 - close to 3,000 if we include the 298 victims of the MH17 (Malaysian airliner) plane crash,” he said.
The death toll was nearly 400 more than that given in the report, which covered the period up to August 17th.
At an emergency meeting of the UN Security Council, US Ambassador Samantha Power poured scorn on Moscow's declarations its forces were not involved in Ukraine.
“It has manipulated. It has obfuscated. It has outright lied,” she said.
“The mask is coming off. In these acts, these recent acts, we see Russia’s actions for what they are: a deliberate effort to support, and now fight alongside, illegal separatists in another sovereign country.”
British UN Ambassador Mark Lyall Grant told the meeting: “Formed units of the armed forces of the Russian federation are now directly engaged in fighting inside Ukraine against the armed forces of Ukraine. These units consist of well over 1,000 regular Russian troops equipped with armored vehicles, artillery and air defense systems.”
Russian foreign minister Sergei Lavrov said today that allegations Russia’s military is fighting in eastern Ukraine are “conjecture”.
“We’re hearing various conjectures, not for the first time, but not once have any facts been presented to us,” he said at a news conference.
Russia’s UN ambassador Vitaly Churkin, responded: “There are Russian volunteers in eastern parts of Ukraine. No one is hiding that.”
Moscow has said some Russians have, in their own time, gone to Ukraine to support the cause of the separatists.
Mr Churkin said he had a message for the United States: “Stop interfering in the internal affairs of sovereign states.”
Mr Obama, who will visit Russia's tiny neighbor Estonia before attending a Nato summit in Wales next Thursday and Friday, said Russian president Vladimir Putin had ignored opportunities to find a diplomatic solution.
In Estonia, he said he would “reaffirm our unwavering commitment to the defense of our Nato allies.”
The White House said Ukrainian president Petro Poroshenko would meet with Obama at the White House on September 18th in a visit that "will highlight the United States' firm commitment to stand with Ukraine as it pursues democracy, independence, and stability."
Mr Obama spoke by phone yesterday with German Chancellor Angela Merkel, who has played a big role trying to resolve the crisis.
The White House said the two agreed the United States and Europe should consider more sanctions.
The United States and European countries have imposed increasingly stiff sanctions on Russia over its annexation of Crimea in March and its role in subsequent fighting in Ukraine.
Asked directly if he would refer to the Russian intervention as an invasion, Mr Obama said: “I consider the actions that we’ve seen in the last week a continuation of what’s been taking place for months now.”
“The separatists are backed, trained, armed, financed by Russia. Russia determined that it had to be a little more overt in what it had already been doing, but it’s not really a shift,” he said.