Ukraine's energy minister has said the country's power infrastructure is under "under massive enemy attack" after a countrywide air raid alert was declared due to incoming missiles.

Russia has launched a "massive" attack on Ukrainian energy and water infrastructure on Thursday, with people urged to take shelter from the barrage.

Israeli military strikes have killed at least 17 Palestinians across Gaza this morning, medics said, as forces stepped up bombardments on central areas and pushed tanks deeper in the north and south of the enclave.