By John Kruzel and Andrew Chung

WASHINGTON, Oct 5 (Reuters) - The US Supreme Court opened its new nine-month term on Monday by hearing a bid by oil companies ExxonMobil and Suncor Energy to thwart a lawsuit by officials in Boulder, Colorado, seeking monetary damages for harms ‌caused by climate change.

US-based Exxon and Canada-based Suncor appealed after the Colorado Supreme Court let Boulder's lawsuit accusing them of state law violations ‌proceed. President Donald Trump's administration has backed Exxon and Suncor, arguing that the federal government's authority to regulate air pollution precludes Boulder's claims.

"This case involves an unprecedented effort to use state law to ​regulate global conduct," Kannon Shanmugam, a lawyer for the oil companies, told the justices.

Boulder is suing the oil companies under Colorado law, Shanmugam added, "on the theory that their global conduct ...