The flag of the U.S. flies outside the U.S. consulate in St. Petersburg, Russia, July 31, 2017. (Xinhua/REUTERS)

WASHINGTON, March 29 (Xinhua) -- U.S. State Department tweeted on Thursday that Russia's decision to expel 60 U.S. diplomats was a "regrettable, unwarranted" one.

Russia will expel 60 U.S. diplomats and shut U.S. consulate in St. Petersburg in tit-for-tat retaliation for Washington's moves against Moscow over an alleged ex-spy poisoning incident in Britain, the Russian Foreign Ministry said earlier on Thursday. The 60 diplomats must leave Russia by April 5.

U.S. State Department tweets on Russia's decision to expel U.S. diplomats.

"It is clear that Russia is not interested in dialogue about issues that matter to our two countries," the U.S. State Department tweeted.

It added that Moscow "is further isolating itself" with its expulsion action following the poison attack in Britain against an ex-Russian intelligence official and his daughter.

Russian Foreign Minister Sergei Lavrov said Russia was expelling the same number of diplomats as the U.S., which on Monday ordered out 60 Russian diplomats and closed Russia's consulate in Seattle.