US President Barack Obama said no settlement will be possible as long as Russia continues to send troops to Ukraine "disguised as separatists".
Obama said during a press conference in Estonia: "We have consistently supported the effort of President Poroshenko to achieve a meaningful ceasefire that could lead to a political settlement of the conflict.
"So far it hasn't helped, either because Russia hasn't been serious about it or has pretended that it's not controlling the separatists."
US President Barack Obama said Russia has "paid a heavy price for its actions" in Ukraine.
Obama commended his hosts Estonia for being "such a strong voice" in both Nato and the EU "on behalf of the Ukrainian people".
"Because we have stood together Russia has paid a heavy price for its actions," he added.
Authorities in the US state of Connecticut are investigating a possible threat against President Obama, according to local media reports.
A statement from the US Secret Service, which oversees the President's personal security, said: "Information has been received by law enforcement regarding a potentially suspicious person and vehicle. We are working with our local law enforcement partners to determine the validity of the information provided."
A local newspaper said state police were looking for a man who had allegedly made a threat against Obama.
He was believed to have been driving a car with Connecticut licence plates.
Obama was making a number of fundraising appearances in the north-east of the country on Friday.
The White House insists President Obama stands by his decision to wear the tan suit that sparked a social media frenzy yesterday.
"I know that there is at least one aspect of the President's news conference that attracted some attention," press secretary Josh Earnest told reporters.
"The President stands squarely behind the decision he made yesterday to wear his summer suit," he joked.
After he wore an unusual tan-coloured outfit during a press briefing, Twitter users were quick to poke fun at the US President.Read the full story ›
US President Barack Obama has warned that Russia faces "more costs and consequences" if it continues to aid rebels in eastern Ukraine.
In a news conference at the White House, he said:
The violence is encouraged by Russia. The separatists are trained by Russia. They are armed by Russia. They are funded by Russia. Russia has repeatedly and deliberately violated the sovereignty and territorial integrity of Ukraine, and the new images of Russian forces inside Ukraine make that plain for the world to see ...
As a result of the actions Russia has already taken, and the major sanctions we have imposed with our European and international partners, Russia is already more isolated than at any time since the Cold War ... This ongoing Russian incursion into Ukraine will only bring more costs and consequences for Russia.
President Barack Obama said all Americans "feel the ache" of the loss of James Foley, the US journalist beheaded in a video released by Islamic State militants.
Obama said Foley was "a man who lived for his work, who courageously told the stories of his fellow human beings and was liked and loved by friends and family."
"All of us mourn his loss," the President said.
President Barack Obama has stressed that Islamic State "speaks for no religion".
"No just God would stand for what they did yesterday and what they do every single day," he said in response to the video released showing the beheading of US journalist James Foley.
"Isil has no ideology of any value to any human beings their ideology is bankrupt," Obama said. "Isil has no place in the 21st Century."
President Barack Obama has said the "entire world is appalled" by the murder of US journalist James Foley.
"Jim was taken from us in an act of violence that has shocked the conscience of the whole world," Obama said at a press conference.
US intelligence officials earlier confirmed that the Islamic State video of US journalists James Foley and Steven Sotloff - who is still believed to be held captive - was authentic.
US President Barack Obama has said he does "not expect there to be an additional operation to evacuate people" from Mount Sinjar in Iraq.
In a statement delivered at the White House, he said that "the situation on the mountain has greatly improved".