(Adds air raid alerts declared across all of Ukraine, fresh comments by Kyiv mayor)

June 2 (Reuters) - Air raid alerts were declared across all of Ukraine early on Friday in the wake of Russian missile launches, official websites showed, and authorities in Kyiv reported two separate waves of attacks.

Russia has launched around 20 separate missile and drone strikes against Ukrainian cities since the start of May.

"There are explosions in the city. Air defences are working," Kyiv Mayor Vitali Klitschko said in a message. Minutes later he added: "More explosions in the city".

(Reporting by David Ljunggren; Editing by Jacqueline Wong & Shri Navaratnam)