By Carolyn Cohn LONDON (Reuters) – Global stocks hit three-week lows and oil rose on Monday as worries increased that Russia will invade Ukraine. Russian forces killed a group of five saboteurs who breached the country’s southwest border from Ukraine on Monday, news agencies quoted the military as saying, an accusation that Kyiv dismissed as the latest in a series of fakes. Kyiv and the West fear that a border incident near eastern Ukraine could be used as a pretext for Moscow to attack its neighbour. Russia denies such plans. Markets are on high alert for any escalation in the crisis. MSCI’s …