May 7 (Reuters) - A number of blasts occurred in several places across the Russia-annexed Crimea early on Sunday, according to Russian and Ukrainian media, with Russian social media reporting that air-defence systems were repelling attacks.

Baza, a Telegram channel with links to Russia's law enforcement agencies, reported that Ukraine sent a series of drones into the Crimean Peninsula, with Russian air defence shooting down at least one over the port of Sevastopol.

According to the channel's preliminary information, there were no casualties.

According to Ukrainian monitoring Telegram channels, explosions took place in Sevastopol and Saki - where Russia has an air base - as well as a few other places on the Crimean Peninsula that Russia annexed in 2014.

Reuters was not able to independently verify the reports.

Strikes on Russian-held targets have intensified in the past two weeks, especially in Crimea. Ukraine, without confirming any role in those attacks, says destroying infrastructure is preparation for its planned ground assault.

(Reporting by Lidia Kelly in Melbourne; Editing by Kim Coghill)