Two boys have been killed in western Melbourne in what police suspect is a series of targeted attacks.

The youths were fatally stabbed in the suburb of Cobblebank on Saturday evening, detectives said.

A 12-year-old boy with critical injuries was found by emergency services on Marble Drive about 8pm and later died at the scene.

Shortly afterwards a seriously injured 15-year-old boy was given treatment nearby on Cobble Street but he also died.

Officers said they believed the two fatal attacks were connected but the exact circumstances were still being determined.

“At this time police are treating it as a targeted attack and the investigation remains ongoing,” police said.

“Too many Victorians have been victims of crime,” Victorian Opposition Leader Brad Battin said in a statement.

“Last night, two more Victorians were tragically added to that tally.”

—AAP