WASHINGTON, April 22 - U.S. Secretary of State John Kerry told Russian Foreign Minister Sergei Lavrov in a telephone call on Tuesday that Washington would impose more sanctions on Russia if tensions did not de-escalate in eastern Ukraine, a senior U.S. official said, Reuters reported.

The official said Kerry talked to both Lavrov and Ukrainian Prime Minister Arseny Yatseniuk.

"With Foreign Minister Lavrov, the secretary expressed deep concern over the lack of positive Russian steps to de-escalate, cited mounting evidence that separatists continue to increase the number of buildings under occupation and take journalists and other civilians captive," he said.