A Russian request for a meeting with Boris Johnson to discuss the nerve agent attack on former double-agent Sergei Skripal and his daughter Yulia has been dismissed as a "diversionary tactic" by the UK.
The Foreign Office confirmed that it had received a request from the Russian Embassy for a meeting with Mr Johnson, one of the most vocal Government critics of Vladimir Putin's regime over the attempted assassination.
The Russian government said it hoped the UK would "engage constructively" with the request for ambassador Alexander Yakovenko to have face-to-face talks with Mr Johnson.
The latest exchanges in the diplomatic spat came as speculation mounted that the Skripals could be able to offer officers investigating the Salisbury nerve agent attack missing clues as the pair continue to recover.
In a statement posted on its website on Saturday, the Russian Embassy said "interaction" between it and the Foreign Office was "utterly unsatisfactory".
They added: "We believe that it is high time to arrange a meeting between Ambassador Alexander Yakovenko and Foreign Secretary Boris Johnson in order to discuss the whole range of bilateral issues, as well as the investigation of the Salisbury incident.
"Ambassador Yakovenko has already sent a respective personal note to the Foreign Secretary.
"We hope that the British side will engage constructively and that such meeting is arranged shortly."
We believe that it is high time to arrange a meeting between @Amb_Yakovenko and Foreign Secretary @BorisJohnson in order to discuss the whole range of bilateral issues, as well as the investigation of the Salisbury incident. https://t.co/hOHA18Lclf pic.twitter.com/cS8XMDiXM7— Russian Embassy, UK (@RussianEmbassy) April 7, 2018
Moscow has denied being responsible for the poisoning of the Skripals but the incident has plunged diplomatic relations between Russia and the West into the deep freeze.
A Foreign Office spokesman said: "It's Russia's response that has been unsatisfactory.
"It's over three weeks since we asked Russia to engage constructively and answer a number of questions relating to the attempted assassinations of Mr Skripal and his daughter.
"We will of course consider their request and respond in due course."
Whitehall sources said Russian foreign minister Sergey Lavrov had turned down the chance for discussions and dismissed the embassy's move as the "latest in a series of Russian disinformation attempts".
Mr Skripal, 66, and his 33-year-old daughter Yulia were left fighting for their lives in hospital after being found unconscious on a park bench in Salisbury on March 4.
The former double agent is "responding well to treatment, improving rapidly and no longer in a critical condition", Salisbury District Hospital said.
The Russian Embassy had previously said it hoped the improvement in the Skripals' health will "contribute to the investigation of the crime perpetrated against them".
Ms Skripal made her first public comments on Wednesday shortly after Russian TV reported that she had contacted her cousin Viktoria in Moscow to say she and her father were recovering and that she would soon be discharged.
The UK authorities have refused to grant Viktoria Skripal a visa to come to Britain, with the Home Office saying her application "did not comply with the immigration rules", prompting a suggestion from the Russian side that the British had "something to hide".
- Digital Desk and Press Association