"Also, simply expelling 23 British diplomats probably won't be enough", Gabuev said.
The pledge comes as 23 British diplomats based in Russia begin packing their bags as they are expelled from the country in retaliation for Russian representatives being told to leave the UK.
Meanwhile he said the use of the Novichok nerve agent, a rare chemical weapon developed by the Soviet Union, had been picked because it sent a signal in its "blatant Russian-ness".
On Friday, British Foreign Secretary Boris Johnson said it was overwhelmingly likely that Russian President Vladimir Putin himself had made the decision to use a military-grade nerve toxin to strike down Skripal.
"The moment you mix this stuff up, it presents a high risk to you and if you were to spill it, you'd be in bad danger", said Andrea Sella, a professor of inorganic chemistry at University College London.
"We think it overwhelmingly likely that it was his [Putin's] decision to direct the use of a nerve agent on the streets of the United Kingdom, on the streets of Europe, for the first time since the second world war".
Russian Federation denies it was involved.
That deadline passed, met only by a series of Russian denunciations and media venting of a conspiracy theory that it was all the work of British intelligence in the first place.
He said: "There is a reason for choosing Novichok".
Britain may find itself on its own in this struggle with Russian Federation, with only the rhetorical support of its allies. "Unlike them, grabbing the microphone in order to accuse Russian Federation of everything", Lavrov said.
"I'm absolutely certain that Russian Federation has underestimated the resolve and unity of North Atlantic Treaty Organisation allies when we have implemented different kinds of sanctions over the last years", Mr Stoltenberg added.
Earlier today, Kremlin spokesperson Dmitry Peskov called the UK's reaction to the attack on the ex-spy "irresponsible".
De Bretton-Gordon said it was possible that the Novichok arrived in Salisbury in Yulia Skripal's suitcase, but said much could go wrong in such a scenario.
European Council President Donald Tusk said Wednesday that the attack was "most likely" inspired by Moscow and announced he would put the issue on the agenda at an EU leaders' summit next week.
Wiltshire Police said 131 people had been identified as potentially being exposed to the nerve agent - but none has shown any symptoms.
Mrs May said on Monday the Government had concluded it is "highly likely" Russian Federation was responsible for the attack which left Mr Skripal, 66, and his 33-year-old daughter in a critical condition in hospital.
But German Defence Minister Ursula von der Leyen said Germany was waiting for an evaluation by United Nations chemical weapons experts of the evidence held by the UK.
He criticised the lack of transparency and said: "Nobody saw even the pictures of these people in a hospital, whether they are alive or maybe they are in good health".
He added: "The British keep hiding the medical assessment from us, we do not have access to the patients, we do not have a chance to talk to the doctors".
Britain's Foreign Office said Saturday that "Russia's response doesn't change the facts of the matter - the attempted assassination of two people on British soil, for which there is no alternative conclusion other than that the Russian State was culpable".
At the White House, Trump said the nerve-agent attack is "something that should never ever happen".
The officials said the Russian hackers chose their targets, obtained access to computer systems, conducted "network reconnaissance" of systems that control key elements of the USA economy and then attempted to cover their tracks by deleting evidence of their infiltration.