Russia's ambassador to the United Nations has given a blistering indictment of the British government's allegations that Moscow was behind the nerve agent poisoning in England of an ex-spy and his daughter.

UN Ambassador Vassily Nebenzia opened a meeting of the UN Security Council on Thursday with a lengthy statement in which he claimed that Russia was the victim of a hasty, sloppy and ill-intentioned defamation campaign by Britain and its allies.

Sergei Skripal, 66, and his daughter Yulia, 33, were found slumped unconscious on a public bench in the southern English city of Salisbury on March 4. London has blamed Russia for the attempted killings, while Moscow denies any involvement.

British police believe the nerve agent was left on the front door of the modest home in Salisbury where Skripal, a former colonel in Russian military intelligence who betrayed dozens of Russian agents to Britain's MI6 spy service, lived after he was exchanged in a spy swap.

The attack has driven Moscow's relations with the West to a new post-Cold War low, with Britain and its allies, including the United States and Canada, expelling about 130 diplomats and the Kremlin responding in kind.

Nebenzia said Thursday that "Great Britain refuses to co-operate with us on the pretext that the victim does not co-operate with the criminal ... A crime was committed on British territory, possibly a terrorist act, and it is our citizens who are the victims."

'Propaganda war'

Nebenzia challenged Britain to take his statement as "a litmus test" of the country's integrity and respect for international norms, saying at one point that the U.K. was trying to delegitimize Russia with its accusations.

Envoy says U.K. trying to discredit, delegitimize Russia 1:18

Britain's ambassador to the United Nations slammed Russia's attempts to impugn its investigation, telling the UN Security Council that the U.K. has acted appropriately throughout the investigation.

Ambassador Karen Pierce said the investigation into the poisoning has been consistent with the convention on chemical weapons.

The country had nothing to hide, she said, adding that she wonders if Russia has something to fear.

UN envoy from U.K. stands by probe into poisoning 1:38

Her speech came after Russia's envoy to the UN took aim at the U.K.'s handling of the investigation. The envoy disputed British claims about Russian involvement, slammed Foreign Secretary Boris Johnson and said there is a "propaganda war" being waged against Russia.

He also asked why Russia hadn't been granted consular access to the victims of the attacks.

On Wednesday, Russia lost its call for a joint inquiry to be held into the poisoning at a meeting of the global chemical weapons watchdog, the Organization for the Prohibition of Chemical Weapons.

While scientists at the Porton Down biological and chemical weapons laboratory near Salisbury have concluded the toxin was Novichok, its chief executive said on Tuesday they it has not yet been determined whether it was made in Russia.

Britain said there is no plausible explanation other than that Russia was behind the attack, and its foreign secretary has accused Russia of running a disinformation campaign. However, even some allies have said Britain needs to provide more evidence about Russian culpability after the Porton Down head's remarks.

Skripal's daughter recovering

Meanwhile, British police have released the first public comments from Yulia Skripal, quoting her as saying she's getting stronger by the day.

The attack left the Skripals in critical condition and doctors had initially feared that even if they did survive, they might suffer permanent brain damage.

Yulia Skripal's condition has improved since she was poisoned earlier this month, British police said in a statement Thursday quoting the 33-year-old. Investigators found traces of nerve agent at the park where she was found and at the home of her father, former Russian spy Sergei Skripal. (Facebook)

However, while her father remains critical but stable in intensive care, Yulia's health has improved rapidly in the last few weeks. In the statement released Thursday, she thanks hospital staff and the people who came to her help "when my father and I were incapacitated."

Her recovery means she can help British counterterrorism police with their investigation, although in the brief statement, no details were offered about what had happened.

'Strength is growing daily'

"I woke up over a week ago now and am glad to say my strength is growing daily. I am grateful for the interest in me and for the many messages of goodwill that I have received," said Yulia Skripal.

"I am sure you appreciate that the entire episode is somewhat disorientating, and I hope that you'll respect my privacy and that of my family during the period of my convalescence."

Former Russian military intelligence colonel Sergei Skripal, shown during a court proceeding in Moscow in 2006, remains in critical condition in a British hospital after he and his daughter were poisoned. (Yuri Senatorov/Kommersant/AFP/Getty Images)

Earlier on Thursday, Russian state TV and Interfax reported that Yulia had phoned her cousin Viktoria Skripal in Russia, saying she and her father were both recovering and that she expected to leave hospital soon.

"Everything is fine, everything is fixable, everyone is getting better, everyone is alive," they quoted her as saying in the call.

Russian state TV said it could not vouch for the authenticity of the quotes. Viktoria, Skripal's niece has said she plans to travel to England to try to bring Yulia back to Russia if she can get a visa.