Republicans captured a majority in the US Senate on Tuesday in a sweeping midterm election victory that delivers a sharp rebuke to President Barack Obama's Democrats.

With crucial wins in North Carolina and Iowa, the Republican Party picked up seven Senate seats to claim a majority in the 100-seat upper chamber, TV networks said.

As results trickled in, Republicans were expected to control at least 52 Senate seats after also defeating Democratic incumbents in Montana, Colorado, West Virginia, South Dakota and Arkansas.

The outcome of the elections suggested Obama would face a tougher final two years in office, complicated by greater Republican power, and influence in Washington.

"This is what tends to happen two years before the end of a presidency," said FRANCE 24's Washington correspondent, Philip Crowther. "Any incumbent president will get punished."

Speaking soon after the results were announced, Republican Senate leader Mitch McConnell said the elections were an indictment of the president.

"This campaign wasn't about me or my opponent, it was all about a government that people no longer trust to carry out its basic duties," McConnell declared upon securing a sixth term as Kentucky senator.

Key Republican wins

The veteran Republican beat Democrat Alison Lundergan Grimes in a race that had looked extremely close until McConnell pulled ahead in the polls in recent days.

In Arkansas, Republican challenger Tom Cotton defeated Democratic incumbent Mark Pryor, despite frantic get-out-the-vote efforts by former President Bill Clinton, who hails from Arkansas.

Along with Cotton, Republicans Shelley Moore Capito in West Virginia, Mike Rounds in South Dakota, Cory Gardner in Colorado and Steve Daines in Montana also won.

France24