The United States has warned Russia that it would be a "grave mistake" to embark on military intervention in Ukraine.
"I don't think there should be any doubt whatsoever that any kind of military intervention that would violate the sovereign territorial integrity of Ukraine would be a huge - a grave mistake," US Secretary of State John Kerry said.
More top news
A possible ninth planet at the edge of the solar system could be the reason behind one of the biggest mysteries in astronomy.
Philip Thomas was a 10-year-old pupil at Pantglas Junior School in Aberfan when a coal tip collapsed and slid downhill.
The chief executive's resignation comes amid controversy about allegations of doping in cycling.