Salisbury poisoning suspects Alexander Petrov and Ruslan Boshirov 'were held in Netherlands'

Two men suspected of poisoning an ex-Russian spy were detained briefly in the Netherlands earlier this year, according to research by investigators Bellingcat.

An unnamed security official was quoted by Bellingcat as saying that Alexander Petrov and Ruslan Boshirov were released without being charged.

Dutch authorities have not yet confirmed the report and said that they were assessing a request for comment.

Petrov and Boshirov have been named by Britain as the prime suspects behind the attempt to kill Sergei Skripal and his daughter Yulia with the Soviet-designed nerve agent novichok.

They were both found slumped on a bench in Salisbury in March and were critically ill in hospital. They have since been discharged.

It was reported last week that two unidentified Russian spies were arrested on Dutch soil and deported.

Leaked police information linked the arrests with attempts to smuggle hacking equipment to Switzerland.

It was also claimed that Petrov had made previous visits to the UK in 2016 and 2017.

The British government concluded that the men were from Russia's military intelligence agency, the GRU

Russian president Vladimir Putin earlier this month said that the suspects had been identified and they were civilians not linked to the government.

Mr Putin said: "We know who they are, we have found them. There is nothing special or criminal about it, I can assure you."

The Russian president denied they worked for the military and described them as "civilians".

Last week, Petrov and Boshirov denied being Russian operatives or being involved in the Skripals' poisoning.

They told Russia Today they were only in Salisbury as tourists to visit the cathedral and nearby Stonehenge.

Police published a detailed photographic account of the men's movements while in the UK.

An Interpol "red notice" and a European arrest warrant have been issued for their arrest should they try to leave Russia.