The lab's chief added that it only sought to test the chemical used on Sergei Skripal and his daughter, not decide its source. Still, Russia called the remark proof the U.K. is fabricating its claims.
Tensions between Russia and the West are ratcheting up as the Russian Foreign Ministry announced the expulsion of the officials and the closure of the U.S. Consulate in St. Petersburg.
Thousands gathered in Kemerovo to protest the official response to the blaze, which reportedly killed dozens of children. Four people have also reportedly been detained for questioning.
The move follows the poisoning of former Russian spy Sergei Skripal and his daughter in the U.K. earlier this month. The Russians have been given seven days to leave the country.
In an interview with the BBC, U.S. Army Gen. John Nicholson has reiterated charges that the Kremlin is providing arms to the Afghan resistance. Moscow calls the accusation "idle gossip."
At a summit in Brussels, EU leaders said "there is no plausible alternative explanation" for the poisoning of Sergei Skripal and his daughter earlier this month in southern England.
John Dowd recently said the special counsel's Russia investigation should be shut down. He is now leaving, saying, "I love the president and wish him well."
Former U.N. ambassador John Bolton, rumored as a candidate for national security adviser, appeared in a 2013 video for a Russian gun rights group founded by a Putin ally close to the NRA.