KYIV, Ukraine — Ukraine said Tuesday that it had struck the Crimean bridge for the third time since the start of Russia’s full-scale invasion, after spending months planting explosives on support structure beneath the water.

The extent of the damage was not immediately clear, but the Security Service of Ukraine, the intelligence agency known as the SBU, released a statement and a video that it said showed one of the detonations.

“Today, at 4:44 a.m., without any civilian casualties, the first explosive device was detonated,” the agency said in a statement. “The underwater support pillars were severely damaged at the seabed level — aided by the equivalent of 1,100 kg of TNT.”

Surveillance footage released by the agency and verified by The New York Times shows an explosion under the Kerch Strait Bridge, which connects Russia’s mainland and the Crimean peninsula. The attack appeared to target support features of the bridge. It was not immediately clear how much damage the bridge sustained. A photo from the agency shows some damage to its railing. Traffic on the bridge was suspended for about three hours Tuesday morning, and then later in the day.A Russian military blog, Rybar, run by a former Russian army service member, Mikhail Zvinchuk, said in a Telegram post that a Ukrainian underwater drone had attacked the bridge early Tuesday but that it had hit only a defensive barrier around one of the pylons. Debris fell on the road above, Rybar said in the post.