British Prime Minister David Cameron has reiterated the possibility of tightening sanctions against Russia.

"If Russia takes a positive approach towards Ukraine's freedom and responsibility we could see those sanctions removed, if Russia continues to make matters worse then we could see those sanctions increased, it's as simple as that," he told reporters on Friday in Brisbane, where he arrived for the G20 summit.

He also added: "I still hope that the Russians see some sense and recognize that they should allow Ukraine to develop as an independent and free country, free to make its choices."