Traffic was stopped on the Russian-built Crimean Bridge due to "an emergency" situation, Russia-installed officials said on Monday, while Ukrainian media reported blasts on the bridge.
Sergei Aksyonov, a Russian-installed governor, said the emergency occurred on the 145th pillar of the bridge which links the Crimean peninsula to the Russian region of Krasnodar. He did not provide any further detail.
The RBC-Ukraine news agency reported that explosions were heard on the bridge.
Crimea was annexed by Russia from Ukraine in 2014, but is internationally recognised as part of Ukraine.
Russia's Grey Zone channel, a heavily followed Telegram channel affiliated with the Wagner mercenary group, reported that there were two strikes on the bridge at 03:04 a.m. (0004 GMT) and 03:20 a.m.
Reuters was not able to independently verify the reports. There was no immediate comment from Ukraine.
It was not immediately clear what the incident on the bridge would mean for the U.N.-brokered deal that allows the safe Black Sea export of Ukrainian grain. The deal is due to expire on Monday and was still in limbo as of Sunday night.
The 12-mile (19-km) road and rail bridge was damaged by an explosion last October, in an attack that the Kremlin said had been orchestrated by Ukrainian security forces. Ukraine admitted only indirectly to the attack months later.
Both Aksyonov and the governor of the Krasnodar region, Veniamin Kondratyev, said that they set up operational headquarters in their regions to address the emergency situation on the bridge.
The Russian-backed administration of the peninsula said Crimea is provided with all necessary stock, but urged residents not to travel via the bridge.
Serhiy Bratchuk, spokesperson for Ukraine's Odesa military administration, posted a photo on his Telegram of what seemed a line of the bridge in distance, broken in the middle.
It was not immediately clear whether that was related to the attack.