WASHINGTON (AFP) - The 60 US envoys who were expelled by Russia amid a diplomatic crisis triggered by the poisoning of a former spy have left the country, the State Department said on Thursday (April 5).

"This morning 60 American diplomats left Russia in compliance with the Russian government's unwarranted decision to declare them persona non grata," a US spokeswoman said.

The Americans were ordered out by President Vladimir Putin's Kremlin after Washington responded to a nerve agent attack on a former Russian spy in Britain by expelling 60 Russians.

Washington alleged that the Russians - 48 attached to the Russian embassy and 12 to Moscow's UN mission - were intelligence agents working under diplomatic cover.

Moscow denies this, just as it denies having any hand in poisoning former double agent Sergei Skripal on British soil. Washington insists the expelled Americans are State Department employees.

"We regret Russia's decision to expel our diplomats, dedicated professionals who have represented the United States with distinction in an effort to build bridges between our two countries, so that we might find a way to confront shared challenges together," the official said.