The international chemical weapons watchdog has rowed back on a suggestion that up to 100 grams of liquid nerve agent were used in the attack on former Russian spy Sergei Skripal and his daughter.
The head of the Organisation for the Prohibition of Chemical Weapons (OPCW), Ahmet Uzumcu, told the New York Times the amount of Novichok used indicated it was deliberately applied as a weapon.
However, in a statement, an OPCW spokesman said it was not able to "estimate or determine the amount of the nerve agent that was used" in the incident in Salisbury on March 4.
The spokesman added however: "The quantity should probably be characterised in milligrams."
Earlier Mr Uzumcu told the paper the Novichok could have been applied as a liquid or aerosol.
He said: "For research activities or protection you would need, for instance, five to 10 grams or so, but even in Salisbury it looks like they may have used more than that, without knowing the exact quantity, I am told it may be 50, 100 grams or so, which goes beyond research activities for protection.
"It's not affected by weather conditions. That explains, actually, that they were able to identify it after a considerable time lapse."
He added the samples collected suggested the nerve agent was of "high purity".
The OPCW statement came as Czech president Milos Zeman disclosed that his country had produced small quantities of Novichok.
Britain has argued the use of Novichok - which was developed by the former Soviet Union in the 1980s - meant there was no "plausible alternative" explanation other than the Russian state was behind the attack.
However Mr Zeman's comments were seized on by President Vladimir Putin's spokesman Dmitry Peskov who said they were a "clear illustration of the groundless stance the British authorities have taken".
The Czech president is known for pro-Russia views, although his country joined other nations in expelling Russian diplomats as a result of the poisoning.
Moscow has denied accusations it was responsible for the poisoning of the Skripals but the incident plunged diplomatic relations between Russia and the West into the deep freeze.
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.
The inquiry into the nerve agent attack in the Wiltshire city has involved 250 detectives who have gone through more than 5,000 hours of CCTV and interviewed more than 500 witnesses.