Ukraine’s security service, the SBU, said on Telegram that its agents had mined the piers of the road and rail Crimean Bridge, also called the Kerch Bridge, and detonated the first explosive at 4.44am on Tuesday (11.44am AEST).

The whole operation took several months, it added.

The agency said it had used 1100 kilograms of explosives which “severely damaged” the underwater pillars supporting the bridge.

Traffic on the bridge was suspended early on Tuesday morning, then again mid-afternoon, before resuming shortly before 6pm local time (1am Wednesday AEST).

Although the scale of the damage was not immediately clear, Tuesday’s attack is the latest example of the SBU’s attempts to blindside Moscow and demonstrate that there are costs to continuing its war.

On Sunday, the SBU launched an audacious drone attack on Moscow’s fleet of nuclear-capable bombers, stationed at various Russian airfields thousands of miles away from Ukraine.

Vasul Malyuk, the head of the SBU, said that attack caused an estimated $US7 billion ($10.8 billion) in damage and had struck 34 per cent of Russia’s strategic cruise missile carriers, which have been used to pummel Ukrainian cities throughout the war.

The SBU said Malyuk had also overseen Tuesday’s attack.

“God loves the Trinity, and the SBU always sees things through to the end and never does the same thing twice. We previously struck the Crimean Bridge twice, in 2022 and 2023. So today we continued this tradition, this time underwater,” Malyuk said.

He stressed that the bridge is a “completely legitimate target,” since Russia uses it “as a logistical artery to supply its troops” fighting in mainland Ukraine.

As well as serving as a vital supply line for Moscow’s troops, the Crimean Bridge also has huge symbolic value for President Vladimir Putin, embodying his objective to bind the Ukrainian peninsula to Russia.

Built after Russia’s annexation of Crimea in 2014, Putin opened the bridge in 2018. The project cost around $US3.7 billion ($5.7 billion).

Tuesday’s attack marks the third time that Ukraine has targeted the bridge since Moscow’s full-scale invasion in 2022.

In October of that year, a fuel truck exploded on the bridge, engulfing a part of it in flames.

In July 2023, the SBU said it had blown up a part of the bridge using an experimental sea drone. Both times, Russia moved quickly to repair the damaged sections.

As well as suspending traffic on the bridge, Russian authorities temporarily halted maritime traffic in the waters off Sevastopol, the largest city in Crimea, according to state media RIA Novosti.