WASHINGTON (AFP) - Republicans pushed close to a majority in the US Senate as midterm election results were being counted on Tuesday, grabbing at least five seats from President Barack Obama's Democrats.
In Colorado, Republican challenger Cory Gardner upset incumbent Democrat Senator Mark Udall, putting the Republican party on the brink of capturing a majority in the 100-member chamber, television network projections showed.
The opposition party needed a net gain of six seats to claim control of the Senate, with results still being tallied in close contests including in Iowa and North Carolina.
Earlier TV network projections showed Republican candidates defeated Democrats in Montana, Arkansas, South Dakota and West Virginia.
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.
In Georgia, Republican David Perdue was projected to get more than 50 percent, avoiding a runoff in three-way race against Democrat Michelle Nunn and Libertarian Amanda Swafford, CNN and CBS reported. The win would keep the Georgia seat in Republican hands.
Republicans also held Kansas, with incumbent Pat Roberts fending off independent challenger Greg Orman, Fox and CBS said.
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.