Russia will face more sanctions if they continue to "destablise" Ukraine, William Hague has said.
The former Foreign Secretary told the BBC that Russian President Vladimir Putin is facing a "huge long-term price" for his country's alleged role in supporting separatists in eastern Ukraine.
"The costs to Russia over this behaviour are mounting and will get even higher," he told the BBC.
"If Russia continues to destabilise Ukraine there will be higher sanctions."
Mr Hague said the UK was not planning to send arms to the Ukrainian government following calls from ex-defence secretary Liam Fox.
"We are not planning to send arms to Ukraine - we want to see a diplomatic solution. You have to think very carefully before you send arms into a conflict."
Thousands of Russians are marching in Moscow to mark the first anniversary of what they viewed as a "coup" in neighbouring Ukraine.
14 soldiers died and many more were injured as Ukraine left the strategically important hub of Debaltseve.
Dramatic footage shows the moment a TV crew were forced to flee a huge explosion after a gas pipeline was hit by mortar fire in Ukraine.