The new president of the European Council could be "very important" for David Cameron.
The mother of the three Australian children killed on flight MH17 told a memorial service her "arms would always be reaching for them."
A woman has apparently posted pictures of herself on social media with mascara looted from the Malaysian Airlines flight MH17 crash site.
Pro-Russian rebels have advanced against government forces during fighting around the airports in Luhansk and Donetsk, as well as moving toward the strategic port of Mariupol.
Separatists also killed two sailors when a Ukrainian naval vessel was hit by artillery fired from the shore - the first such attack since the conflict began in April.
ITV News' Europe Editor James Mates reports from Donetsk:
Nato leaders meeting this week are expected to create "a very high-readiness force" to deal with Russian aggression in Ukraine.
The new force could include several thousand troops that will be mobilised for action in any potential 'hotspot' within 48 hours, according to officials.
Nato already has a rapid reaction force but US President Barack Obama and other leaders meeting for a summit in Wales this week are expected to create a new force that would be able to respond more quickly to a crisis.
– Nato Secretary-General Anders Fogh Rasmussen
We will develop what I would call a spearhead ... a very high-readiness force able to deploy at very short notice. This could include several thousand troops, ready to respond where needed with air, sea and special forces support.
David Cameron says Russia appears to be trying to force Ukraine "to give up its democratic choices at the barrel of a gun".
Speaking in the House of Commons, the Prime Minister said the presence of Russian soldiers on Ukrainian soil is "completely unjustified and unacceptable".
Pro-Russian rebels have said they would be prepared to stay part of Ukraine if they were granted "special status," Russian news agencies report.
In a statement the separatists said one of their key conditions would be for Kiev to immediately end its military offensive.
Ceasefire talks were going ahead today but no major decision was expected.
Andrei Purgin, one of the leaders of the self-proclaimed Donetsk People's Republic, said: "This is the beginning of the process. We have come with proposals to find common ground and end the war and people dying."
The European Union could limit gas use to protect household energy this winter if Russia cuts off its gas supply to Europe over the Ukraine crisis.
Kiev claims Russia has threatened to halt its supply over fears Ukraine could siphon off energy destined for the EU as the pipeline runs through the country.
An EU source told Reuters: "In the short-term, we are very worried about winter supplies in south west Europe. Our best hope in case of a cut is emergency measures to protect households."
On Wednesday the EU is expected to discuss whether to impose new sanctions on Russia if they fail to pull its forces out of Ukraine. If it agrees to do so the sanctions are likely to be financial.
Russia has called for peace in Ukraine as it tries to push for a ceasefire.
Russia foreign minister Sergei Lavrov urged for a new round of talks on the issue and said: "We call for an exclusively peaceful settlement of this severe crisis, this tragedy."
Pro-Russian separatist leader Andrei Purgin said they were willing to discuss the exchange of prisoners and a temporary ceasefire.
Fighting in eastern Ukraine between separatists and the Ukrainian government has been going on since Russia annexed Ukraine's southern peninsula of Crimea in April.
German Chancellor Angela Merkel has said doing nothing in response to Moscow's actions in Ukraine is "not an option".
She said further sanctions should be imposed even if they impacted on German companies.
"Accepting Russia's behaviour is not an option. And therefore it was necessary to prepare further sanctions," she said.
Seven Ukrainian soldiers have been killed in the past 24 hours, a military spokesman has confirmed.
Earlier the military said Ukrainian paratroopers were fighting a Russian tank battalion in a bid to hold onto the airport outside Luhansk, a separatist stronghold on the border with Russia.
But military spokesman Andriy Lysenko said Ukrainian forces have now pulled back from the airport after being ordered to do so.
Russian President Vladimir Putin has said he "hopes common sense will prevail" in the West over sanctions imposed on his country.
European Union leaders have agreed to ask the European Commission to draw up more measures against Moscow after accusations Russia is sending troops into Ukrainian territory.
Ukrainian President Petro Poroshenko has accused Russia of launching a "direct and open aggression" against Ukraine.
He added there would be "high-level personnel changes" within the Ukrainian armed forces in light of the events of the past few days.
This is in spite of ceasefire negotiation talks due to take place later today.