U.S. Senator John McCain is claiming frontrunner status among Republican presidential hopefuls after winning key nominating contests on the day known as "Super Tuesday."
In the Democratic races, Senators Hillary Clinton and Barack Obama each scored key wins but no definitive victory.
McCain beat his Republican rivals in nine states, including three of the nation's most populous -- California, New York and Illinois. He now has more than half of the delegate votes needed to win his party's nomination for president. Just a few months ago, McCain's campaign appeared on the verge of collapse, as public opinion polls showed him trailing badly.
His rivals, former Governors Mitt Romney and Mike Huckabee, each won several states Tuesday, but not enough delegates to put either candidate close to McCain.
Meanwhile, Clinton and Obama traded victories, and neither emerged as the clear Democratic frontrunner.
Clinton victories included the big wins of California, New York and Massachusetts. Obama won more states, but not as many delegates.
Clinton has a slight lead over Obama in the overall delegate race.
Tuesday was the biggest primary voting day in U.S. election history, with 24 states holding primaries or caucuses to choose their Republican and Democratic Party presidential nominees.
Candidates will be allotted delegates to their party's national convention based on the primary election results.
Two-thousand-25 delegates are required to win the Democratic presidential nomination, while 11-hundred-91 are needed to win the Republican nomination.
Some states award delegates for Republicans on a winner-take-all basis, while other states allocate delegates for both parties on a proportional or district-by-district basis.