The arrest of a high-ranking Ukrainian intelligence agent accused of spying for Russia has highlighted the urgent need for a cleanout of the country’s key security service, a former deputy head of the agency has said.

The Ukrainian security service (SBU) reported on Thursday that they arrested a lieutenant colonel in their ranks on suspicion of “high treason” and published a photograph of bundles of cash found in his home.

The unnamed man is said to have used his mobile phone to photograph documents detailing the location of military checkpoints in Zaporizhzhia, a frontline region in the south-east of the country, and sending the information via an email account registered on a Russian domain.

A photo issued alongside the official statement showed sim cards issued by Russian mobile carriers, bundles of foreign currency, a knuckle duster, two knives and a Russian language guide to learning English.

“Evidence of permanent connections with representatives of law enforcement and state bodies of the Russian Federation was also established,” the statement said. “In particular, close relatives of the traitor are among them.”

Maj Gen Viktor Yahun, who was deputy head of the SBU until, 2015, said there needed to a thorough cleanout of the service, which he said had long had an overly close relationship with its Russian counterpart, the FSB.

Following Russia’s invasion on 24 February last year, more than 60 members of the SBU and the prosecutor general’s office had remained in occupied territory and collaborated with the Russian forces, highlighting the scale of the infiltration of Ukrainian law enforcement by the Kremlin.

The arrest of the SBU lieutenant colonel in Zaporizhzhia on Thursday on treason charges. Photograph: SBU

There have also been multiple arrests of SBU agents on counts of treason in the rest of Ukraine over the last 11 months, including Oleg Kulinich, who was appointed by Volodymyr Zelenskiy in 2020 to oversee operations in Crimea, which has been held by Russia since 2014. He is yet to comment.

In October, Ukraine also requested the extradition from Serbia of Andriy Naumov, who used to head the department of internal security at Ukraine’s state security service but who left the country hours before Russia’s invasion. He has not commented.

Yahun said: “Kulinich and Naumov were at the top of the ranks and they had access to the most secret of information.”

As late as 2010, Yahun said the SBU had internally celebrated KGB Day, marking the establishment of the communist-era Russian secret service, and there remained pro-Russian agents through the ranks of the service.

Yahun claimed that the biggest attack on a military site near Lviv in western Ukraine last year had been enabled by a 77-year-old former SBU agent who had passed on the coordinate details and that he feared many in the service still considered themselves Russian.

While the generation that worked for the Soviet security services had retired, Yahun added, the recruitment practices of the SBU meant that their sons and daughters were now in the agency.

“They grew up with the same values as their fathers,” he said. “Ukraine made a major mistake in not following the lead of the Baltic nations following independence in reforming the security services from ground zero.”

“Of course there were always patriots in the SBU, but they have been in the minority,” he said. “It is getting better and since 24 February President Zelenskiy has cleaned the top ranks, so I do not believe any vital strategic information has been passed to Russia. Now they are moving their way down the ranks.”

Yahun said some SBU agents had been bribed and blackmailed into working for Russia, while others were double agents. “Others just regard themselves as Russian,” he said. “There was an arrest of a woman in her 40s working in the SBU who had been found to have been sharing Russian propaganda on social media.”