Nato warns of russian threat to moldova
'Weapons from NATO would aid war crimes in Ukraine'
Russia says weaponry from NATO states will abet war crimes in Ukraine and worsen the situation.
British PM David Cameron said pressure on Moscow would mount if it did not curtail military action.
Pro-Russian separatists attacked a base of the Ukrainian National Guard in an eastern city overnight.
Sentletse Diakanyo says the Western pursuit of economic interests is relentless.
The Ukrainian government denounced the visit as a violation of the rules of diplomacy.
Kiev will in return have to pass tough economic reforms to unlock $14-18 billion in standby credit.
The US and EU agreed to work together to prepare possible tougher economic sanctions.
Obama is concerned at the possibility of further Russian encroachment into Ukraine.
Earlier on Monday, Russian troops forced their way into a Ukrainian marine base.
Barack Obama will seek support for his firm line at a meeting with other leaders of the G7.
The Russians used stun grenades and fired automatic weapons as they charged in to seize the base.
A top military commander says Russian forces pose a threat to the separatist Transdniestria region.