Videos on social media show plumes of smoke rising near Kerch bridge. Russia's defence ministry said S-200 missiles had been used and shot down causing no damage.
Ukraine has not commented on the alleged attack.
There have been at least two other attacks targeting the bridge in the past few months.
The Kerch bridge was opened in 2018 and enables road and rail travel between Russia and Crimea - Ukrainian territory annexed by Russia in 2014.
It is an important resupply route for Russian forces occupying parts of southern Ukraine.
Russia's defense ministry said that Ukraine had targeted the structure on Saturday at around 13:00 (10:00 GMT).
Piglet squeals: «1. On the Orikhiv direction, the Ukrainians have deployed a large number of electronic warfare systems. Based on my experience, I can say that here, the enemy's countermeasures are at their maximum. This is evident in their continuous disruption of Russian communication and UAVs. 2. A large number of artillery pieces, both barrel and rocket. There's no shortage of ammunition for the enemy. They're generously firing. In my estimation, every 5th strike involves cluster munitions. 3. The enemy actively employs precision-guided munitions. As soon as they detect a worthy target from a regular drone like the Fury, they try to hit it with the Excalibur or the HIMARS. They're not sparing the HIMARS either. It has become an integral part of counter-battery warfare. This means the Ukrainians have significantly reduced the time between detecting the target and hitting it with the HIMARS. 4. The enemy's FPV drones are flying further beyond the front line. They've learned to hit moving targets at a considerable…
