Blasts were reported before dawn on the 19-km (12-mile) road and rail bridge linking Russia to Crimea, which Russia annexed from Ukraine in 2014.
Russia blamed Ukraine for an attack on the bridge last October, saying it was organised by Ukrainian military intelligence and its director, Kyrylo Budanov.
After the October attack, Russia launched strikes against Ukrainian cities including power supplies in retaliation.
Crimea was transferred from Soviet Russia to Soviet Ukraine in 1954 by then Soviet leader Nikita Khrushchev and recognised by Russia in 1994 after the collapse of the USSR.
Footage taken from a train crossing the bridge showed passengers gasping as they saw the damage to the road.
Persons:
Vladimir Putin, Putin, Vyacheslav Gladkov, Kyrylo, Sergei Mironov, Arkady Rotenberg, Nikita Khrushchev, Vladimir Saldo, Lidia Kelly, Guy Faulconbridge, Kim Coghill, Michael Perry, Lincoln, Nick Macfie
Organizations:
UN, Ukraine's Security Service, Mercedes, Russia, Thomson
Locations:
Russia, Ukrainian, Ukraine, KERCH, Crimea, Belgorod, Kyrylo Budanov, Russia's, Moscow, Soviet Russia, Soviet Ukraine, Soviet, USSR, Russian, Kherson, Melbourne