WASHINGTON - Republicans edged close to a majority in the US Senate as midterm election results were being counted Tuesday, grabbing at least four seats from President Barack Obama's Democrats.
TV network projections showed Republican candidates defeated Democrats in Montana, Arkansas, South Dakota and West Virginia - gaining four of the six seats the party needs to tilt the Senate balance.
Media forecasts meanwhile said Republicans would keep control of the US House of Representatives, and likely increase their majority.
Analysts have predicted Republicans were likely to control both chambers for the first time since 2006, complicating the last two years of Obama's presidency.
CBS News projected the Republicans would hold at least 226 of the 435 House seats. NBC said the party would take 242 seats.
In the Senate contests, Republicans picked up West Virginia when Shelley Moore Capito won the race for the seat vacated by retiring Democrat Jay Rockefeller.
In battleground state Arkansas, Republican challenger Tom Cotton defeated incumbent Democratic Senator Mark Pryor in the home state of former president Bill Clinton.
And in South Dakota, Republican Mike Rounds defeated Democrat Rick Weiland to take the seat of retiring Democratic Senator Tim Johnson, network projections said.
Montana also flipped to the Republicans, as Steve Daines topped Democrat Amanda Curtis in a seat that had been Democratic.
In Kentucky, Republican Senate minority leader Mitch McConnell was re-elected, according to projections - putting him in line to be the next majority leader if his party gains control of the upper chamber.
Key Senate races in North Carolina and Georgia were so far too close to call.
In North Carolina, Democrat Kay Hagan was battling for re-election against Republican challenger Thom Tillis in the most expensive midterm contest, with spending expected to top $100 million.
A three-way race in Georgia could go down to the wire: with Republican David Perdue, Democrat Michelle Nunn and Libertarian Amanda Swafford fighting for the seat, a runoff will be held if none receive more than 50 per cent.
A runoff was projected in Louisiana, with incumbent Democrat Mary Landrieu and Republican Bill Cassidy leading a field of nine candidates.
In one key hold for the Democrats, Senator Jeanne Shaheen was re-elected in New Hampshire, fending off a challenge from Scott Brown, a former Republican senator in Massachusetts.
The race in Virginia was far tighter than expected, with Senator Mark Warner, a Democrat, and Republican challenger Ed Gillespie running neck-and-neck, networks said.
Races were also reported to be tight in Kansas and Colorado.