June 9 (Reuters) - An attorney for BlackRock ( BLK ) called

antitrust claims by Republican-led states "unprecedented,

unsound and unsupported" on Monday and said they had failed to

show how the firms' involvement with industry climate groups

interfered with market competition.

Gibson Dunn attorney Gregg Costa spoke as BlackRock ( BLK )

and co-defendants Vanguard and State Street seek to

dismiss the claims in the closely watched antitrust case brought

by Texas and 12 other states.