The British foreign secretary, Dominic Raab, said the UK stood in “full support” of the Czech Republic after the country’s police announced they were hunting two Russians, suspected of carrying out the Salisbury poisonings, in relation to an explosion at an arms depot. The Czech authorities said on Saturday they were seeking Alexander Petrov, 41, and Ruslan Boshirov, 43, in connection with a previously unexplained 2014 explosion at a munitions dump in Vrbětice, which left two dead. The duo are believed to be Russian GRU officers – real names Alexander Mishkin and Anatoliy Chepiga. They entered the UK under the names of Petrov and Boshirov in the run-up to the poisoning of former GRU officer Sergei Skripal and his daughter, Yulia, and were also present on Czech territory in October 2014, when the explosion occurred. Raab praised the Czechs, who had “exposed the lengths that the Russian intelligence services will go to in their attempts to conduct dangerous and malign operations in Europe” – and hinted that he believed the same GRU cell was behind both plots. “This shows a pattern of behaviour by Moscow, following the novichok attack in Salisbury,” Raab added. “We are as determined and committed as ever to bring those responsible for the attack in Salisbury to justice, and commend the actions of the Czech authorities to do the same.” Western intelligence sources are confident that the Czech authorities’ investigation is well-founded, and argue that it demonstrates growing evidence of the activities of the 29155 GRU unit, specialising in deadly undercover operations across Europe. Since the election of Joe Biden as US president, the west has become increasingly loud in calling out Russian spy plots. Last week, the US announced the expulsion of 10 Russian diplomats and alongside the UK accused the Kremlin of being behind the the SolarWinds cyberattack. According to Czech media, detectives investigating the explosion initially assumed it was a tragic accident. Two men working at the depot – Vratislav Havránek and Luděk Petřík – died instantly when 50 tonnes of ammunition blew up. Last year, however, investigators from Prague’s counter-intelligence service and the national centre against organised crime received new information. They discovered Mishkin and Chepiga – using the Petrov and Boshirov passports – had been in the country when the explosion took place. The pair flew in from Moscow on 11 October 2014 on a regular Aeroflot flight. They left five days later – the day of the explosion – and went home via Austria. They emailed the depot in advance to arrange a visit and booked into a hotel in the nearby city of Ostrava. The GRU officers sent scanned passports to depot managers issued in two further names – Ruslan Tabarov from Tajikistan and Nicolaj Popa from Moldova. Unusually, their email contained no metadata. The photos matched Chepiga and Mishkin. Police believe the undercover GRU officers visited the arms complex. They have been unable to prove this since all evidence was destroyed. At the time weapons were being unloaded for a delivery to a Bulgarian arms dealer, Emilian Gebrev, who was supplying them to the Ukrainian army. One source told the Czech magazine Respekt that the explosion in the warehouse may have happened prematurely. “It was probably not meant to take place in the Czech Republic, but only later during the transport of weapons to another country,” the source said. Gebrev was poisoned in May 2015 after going for dinner in the Bulgarian capital, Sofia. Bulgarian prosecutors claim three undercover GRU operatives had checked into a hotel overlooking Gebrev’s office. One of them was Sergei Fedotov – real name Denis Sergeev – who flew to London at the time of the Salisbury poisonings. Western intelligence has suspected the same GRU unit of being involved in the poisoning of Gebrev for some time, although the link to the explosion is new. It also believes members of unit 29155 were involved in a failed coup in Montenegro in 2016 and disinformation operations in Moldova in 2014. Around 15 to 20 elite GRU officers are thought to make up the unit, which has a secret HQ in the Skhodnya area of Moscow. It functioned as a diversionary cell, sent deep behind enemy lines, with a base in south-east France, close to the Swiss border. After Salisbury, it appears to have been disbanded. On Saturday the Czech government kicked out 18 Russian diplomats from Moscow’s embassy in Prague. It said it would brief its Nato counterparts at a meeting this week, amid signals that it plans to take a much tougher line over the Kremlin’s regular espionage activities. Russia dismissed accusations that it was behind the 2014 depot explosion as unfounded and absurd. It said it would retaliate for the moves against its embassy staff and on Sunday announced the expulsion of 20 Czech diplomats. It accused Prague of trying to ingratiate itself with Washington by carrying out provocative “anti-Russian actions”. Moscow also denies the GRU was involved in the attempted murders of Sergei and Yulia Skripal. The two men known as Petrov and Boshirov said in a television interview that their visit to Britain in 2018 was innocent. They told the Russian TV network RT they were only in Salisbury as tourists to visit the cathedral, which they described as “famous for its 123-metre spire”. If they visited the site of the poisoning, it was a coincidence, they said. The open-source website Bellingcat revealed Chepiga and Mishkin’s real identities and also discovered they had both been made “heroes of Russia”. Mishkin’s grandmother told neighbours she had a photo of him collecting his award and shaking hands with Russia’s president, Vladimir Putin. It had been thought the decoration was in recognition for Mishkin and Chepiga’s secret work in Ukraine and Crimea, which Moscow annexed in 2014 in a shadowy military operation. It now appears the award may have been connected to the Czech warehouse explosion. The Skripals suddenly fell ill in March 2018, with international investigations confirming they had been poisoned with the novichok nerve agent made by Russia. The Skripals survived the attack, but a British woman, Dawn Sturgess, died after her partner picked up the discarded, modified perfume bottle in which the poison was hidden and gave it to her mistakenly as a gift. Britain has brought a series of charges against the men known as Petrov and Boshirov in relation to the case and an Interpol red notice is outstanding against the two men, requiring other countries to arrest them should they leave Russia.