(Reuters) - U.S. Senate Republican leader Mitch McConnell said on Sunday that President Barack Obama was on the verge of making a "very bad deal" with Iran on its nuclear program and made clear that Congress will weigh in on any agreement.

"Apparently the administration is on the cusp of entering into a very bad deal with one of the worst regimes in the world," McConnell, the Senate majority leader, said on CNN's "State of the Union."

U.S. Secretary of State John Kerry was heading to Switzerland on Sunday to continue negotiations with the Iranians on reaching a deal to contain their nuclear program.

(Reporting by Doina Chiacu; Editing by Frances Kerry)