Alexander Petrov and Ruslan Boshirov, who are wanted for the Skripal novichok attack, are linked to Russian defence ministry

Documents uncovered by investigative journalists have provided the first public evidence that the suspects in the Salisbury novichok attack have formal ties to the Russian ministry of defence.

British authorities have charged Alexander Petrov and Ruslan Boshirov with conspiracy to murder Sergei and Yulia Skripal and Detective Sergeant Nick Bailey. The former Russian spy and his daughter were found collapsed on 4 March; the police officer fell ill after trying to help them. Prosecutors say Petrov and Boshirov work for Russian military intelligence, whichPresident Vladimir Putin has denied.

But a passport information dossier for one of the two suspects bears a “top secret” marking and a telephone number with the order “Do not give information”. The number, called by the Observer on Saturday, links to a reception desk at the Russian defence ministry, where a clerk said he would not speak with journalists or provide any information.

The documents were published by Bellingcat, an online platform that began with investigations of attacks in Syria, and the Russian investigative outlet The Insider. Both sites also specialised in uncovering information about Russian soldiers active in Ukraine since 2014.

Other documents published by the sites included an Aeroflot flight manifest that indicates the two men bought their tickets at the last minute, contradicting their claim that the trip had been planned long ago.

An information page for Petrov obtained by the news outlets gives little biographical information and no data about his past before 2009. Experts say that is extremely rare for a 39-year-old man, and that the department that issued his passport normally only does so for those working in certain roles for the government.

“Normal people don’t get passports here,” Sergei Kanev, an investigative reporter who participated in the research, told TV Rain. “I don’t mean businessmen or high-ranking officials. I mean people who often work undercover, including the intelligence services.”

A Russian foreign ministry spokeswoman rejected the report, writing in a post that she believed Bellingcat had ties to western intelligence, noting its access to a Russian database not publicly available.

In their sole interview last week, two men who resembled the suspects told Russian state-sponsored television that they had visited Salisbury twice but denied they worked for Russian military intelligence, known as the GRU, or had committed any crime. The men said that they were simply tourists on holiday, and had been interested in seeing the spire of Salisbury Cathedral and Stonehenge.

Scotland Yard has said that they believe Petrov and Boshirov to be pseudonyms and that the men’s real identities have been covered up by the Russian government.