LONDON, Feb 17 (Reuters) - British foreign minister Liz Truss will reaffirm support for Ukrainian sovereignty on a trip to Kyiv this week as part of efforts to deter a possible Russian invasion, urging Moscow to end its military buildup along the border.

The United States and NATO said on Wednesday that Russia was still building up troops around Ukraine despite Moscow's insistence it was pulling back, questioning President Vladimir Putin's stated desire to negotiate a solution to the crisis.

Truss will hold talks with Ukraine's Foreign Minister Dmytro Kuleba and will then deliver a speech in Kyiv where she will warn Russia it faces economic pain and global isolation if it invades its former Soviet neighbour.

"I urge Russia to take the path of diplomacy. We are ready to talk," Truss will say, according to extracts of her speech released by her office.

"But we are very clear – if they decide to continue down the path of aggression, there will be massive consequences, bringing Russia severe economic costs and pariah status."

Britain's foreign ministry did not give details of when the trip would happen.

Russia said this week that its forces - part of a huge buildup that has been accompanied by demands to the West for sweeping security guarantees - were pulling back after taking part in exercises in southern and western military districts near Ukraine.

But NATO Secretary-General Jens Stoltenberg said moving troops and tanks back and forth did not amount to proof of a pullout.

Truss will also travel to the annual Munich Security Conference on Saturday where G7 foreign ministers will meet to discuss the ongoing crisis.

(Reporting by Andrew MacAskill, Editing by Rosalba O'Brien)