Sergei Lavrov, Russias top diplomat, described on Thursday UK’s accusations against Moscow over the nerve agent poisoning of ex-spy Sergei Skripal as a mockery of international law and said Russia will push to find out the truth. The Russian Foreign Minister insisted that the poisoning case was fabricated by Britain to "demonize" Russia. Britain has blamed Russia for the March 4 poisoning of Skripal and his daughter in the southern English city of Salisbury. In response, more than two dozen Western allies including Britain, the US and NATO have ordered out over 150 Russian diplomats in a show of solidarity. Moscow has fiercely denied its involvement in the nerve agent attack and expelled an equal number of envoys. "The so-called Skripal case has been used as a fictitious, orchestrated pretext for the unfounded massive expulsions of Russian diplomats not only from the US and Britain but also from a number of other countries who simply had their arms twisted," Lavrov said at a conference in Moscow. "We have never seen such an open mockery of the international law, diplomatic ethics and elementary decorum." Early Thursday, three buses believed to be carrying expelled American diplomats departed from the US Embassy in Moscow. Before the morning departure, journalists outside the embassy compound saw people leaving the residences, placing their luggage on trucks. Some toted pet carriers. Russia last week ordered 60 American diplomats to leave the country by Thursday in retaliation for the United States expelling the same number of Russians. Lavrov noted that Russia will respond in kind to any further hostile moves, but added that "we also want to establish the truth. Moscow called a meeting of the global chemical watchdog on Wednesday over the Salisbury incident, but failed in its bid to join the probe by the Organization for the Prohibition of Chemical Weapons (OPCW). Russia then requested a UN Security Council meeting on Thursday in New York. The chief of Britains defense research lab, the Porton Down laboratory, acknowledged Tuesday it has not been able to pinpoint the precise source of the nerve agent. Gary Aitkenhead said scientists there identified the substance used on Sergei and Yulia Skripal as a Soviet-developed nerve agent known as Novichok. But he added "its not our job to say where that was actually manufactured."