The scooter wouldn’t have looked out of place if it had been parked in front of an apartment block in Moscow, where the electronic two-wheelers are a regular means of transportation for many of the Russian capital’s 13 million residents.

But this one – a key element of an elaborate and deadly operation – was carrying something other than a driver: an explosive device that Russian investigators say was rigged with 100 to 300 grams of TNT.

The bomb was planted near the building on Moscow’s Ryazansky Prospekt by a secret agent on behalf of Ukraine’s brazen state security service, the SBU, people familiar with the attack said.

A hidden camera recorded what came next. The bomb was detonated before dawn as Lt. Gen. Igor Kirillov, the head of Russia’s nuclear, chemical and biological defense forces, was leaving the building with his assistant. The explosion killed both men.

The assassination was the latest blow in an escalating shadow war between Kiev and Moscow, waged by their vast and powerful state intelligence agencies, both successors to the Soviet Union’s intelligence agencies, with the SBU being a direct descendant of the KGB.

Operating behind enemy lines, these authorities have targeted military officials and politicians, sabotaged energy infrastructure and rail systems, and used hybrid warfare tactics, including cyberattacks and disinformation campaigns, to sow chaos within each other’s borders.

On the Ukrainian side, the often controversial SBU, which the US and other allies have long urged Kiev to reform, has been spurred by internal competition with the military intelligence directorate known as GUR. It has become what one intelligence official involved in planning operations called a “liquidator of the Russians.”

An SBU official confirmed that his agency was responsible for Kirillov’s death, calling him a “war criminal” who “gave the order to use banned chemical weapons against the Ukrainian military.” He warned: “Such an inglorious end awaits those who kill Ukrainians.”

The SBU is primarily focused domestically, but since Russia invaded Ukraine in 2014, it has operated within Kremlin-occupied Ukraine and within Russia. Since Moscow’s full-scale invasion in 2022, it has attacked Russia’s Crimean Bridge and destroyed much of its Black Sea Fleet with naval drones.

The intelligence official noted that between 2014 and 2021, several killings of pro-Russian separatist leaders were carried out by Kiev agents in the Moscow-controlled Donetsk and Luhansk regions.

Another intelligence official, who spoke on condition of anonymity, said that the SBU’s own agents operated within Russia’s borders but that it also recruited anti-Kremlin Russians to carry out acts of sabotage and even assassinations. The FSB said on Wednesday it had arrested an Uzbek suspect in connection with Kirillov’s killing.

The SBU has become a crucial tool for Kiev in the fight against Russia on multiple fronts. Russia is having difficulty countering its efforts, said Andrei Soldierov, a senior fellow at the Center for European Policy Analysis. “The FSB (Russia’s main security service) is very good at investigating what has already happened, but not very good at gathering information about what is coming. “It’s a different set of skills,” he said.

“For this, the agency should be a very good information gathering point, that is, there is trust and a good exchange of information – something that you don’t see in Russian agencies.”

Valentyn Nalyvaichenko, a lawmaker who has twice served as SBU chief, said the spy service had collected “a lot of information and counterintelligence data” on Russia’s military and intelligence leadership. It has found ways to plant moles, crack communications within enemy territory and identify vulnerabilities in Moscow’s intelligence network.

Part of the SBU’s effectiveness stems from its enormous size, ironically a result of its Soviet heritage. When Ukraine gained independence in 1991, the SBU absorbed many of the KGB’s structures, resources and responsibilities and did not shrink.

With more than 30,000 employees and even more secret agents, the SBU is almost as big as the FBI with its 35,000 agents. It is more than seven times the size of the British domestic intelligence service MI5 and more than four times the size of the Israeli Mossad.

“One of the main tasks of the Security Service of Ukraine, especially in wartime, is to counteract the enemy’s special services,” said Vasyl Malyuk, head of the SBU, in previously unpublished answers to questions sent by the Financial Times earlier this year.

Malyuk declined to comment directly on operations inside Russia. But he said: “The security service’s position is clear and unequivocal: any crime committed by the attacker must be punished.”

The SBU rarely explicitly claims public recognition for murders. Instead, plausible deniability is often chosen.

In August 2022, the agency planted a bomb in a car belonging to Russian ultranationalist ideologue Alexander Dugin, a close ally of Russian President Vladimir Putin and a supporter of war in Ukraine. But Dugin didn’t drive; His daughter Darya Dugina was behind the wheel and died in the explosion.

The SBU’s work was often controversial. They carried out a fake assassination attempt on a Russian dissident journalist in Kiev in order to allegedly expose a team of hitmen hired by Moscow to destabilize Ukraine. participates in monitoring investigative journalists and activists reporting on suspected corruption within its ranks; and faced several embezzlement scandals.

“(The SBU) has enormous power – some would say too much power,” a Western diplomat told the Financial Times.

The diplomat said the agency had proven largely unresponsive to major reforms for years, despite urging from Ukraine’s biggest backer, the United States, other G7 members and EU states.

But amid the war with Russia, these Western nations have put aside some grievances and strengthened their ties and information sharing. The agency has developed particularly close ties with the CIA, which has invested millions of dollars in training programs for Ukrainian agents.

“What we started in 2014 is now working,” Nalyvaichenko said of working with Western agencies.

The SBU has come a long way since late February 2014, when it was destroyed by former President Viktor Yanukovych after the Euromaidan revolution. Before escaping, Yanukovych ordered a raid on the agency in which his agents stole key state secrets and burned anything they couldn’t get out by car and helicopter.

The SBU, already struggling with trust issues, suffered significant defections in the spring and summer of that year when Russia annexed Crimea and took control of cities in eastern Ukraine.

As then-new SBU director, Nalyvaichenko inherited a fragmented agency full of spies loyal to the Kremlin. Thousands of agents were suspected of collaborating. A purge followed in which the authorities arrested numerous of their own spies and initiated investigations into treason.

“We started from scratch, with the burnt operational files in our backyard at the SBU,” he said.

Nalyvaichenko said Kiev had brought in younger, patriotic agents whose allegiance was to the area within Ukraine’s internationally recognized 1991 borders.

Since Russia’s full-scale invasion began nearly three years ago, hardly a month has gone by without a headline about a Russian official involved in its war effort being eliminated by SBU agents.

Last month, the SBU claimed to have killed Valery Trankovsky, chief of staff of the Russian Black Sea Fleet’s 41st Missile Brigade, in a car bomb attack in occupied Crimea.

But there are times when the credit goes to its sister agency, the Directorate of Military Intelligence, known as GUR. Under the supervision of its enigmatic boss Kyrylo Budanov, the unit has also carried out covert operations and assassinations far beyond enemy lines.

The two agencies vie for glory and try to outdo each other by assassinating high-ranking officials or attacking larger military targets deeper inside Russia. Sometimes they work together.

Not for the first time, the SBU’s work has discouraged the Russian defense establishment. Yuri Kotenok, a Russian war reporter, wrote that Ukraine’s intelligence services “feel like they have complete impunity toward Russia.” He added: “Obviously no one doubted Kiev’s role, but the fact that the enemy is almost openly boasting about it is quite symptomatic.”