Barack Obama joins in the applause at a campaign stop in Houston, Texas, after winning the Democratic primary election in Wisconsin, extending his lead over Hillary Clinton.

But the race for the Democratic presidential nomination is far from over. Mrs Clinton marches on, this time to Ohio. Both Ohio and Texas vote on 4 March.

Voting had taken place in freezing temperatures in the northern state of Wisconsin.

Democratic voters have been inspired by the close contest between the two hopefuls, consistently turning out in greater numbers than Republicans.

And despite the cold, there was again a heavy turnout in many areas. With 97% of the ballots counted, Mr Obama had secured 58% of the vote to Mrs Clinton's 41%.

Mr Obama has won more states, but has only a small lead in delegates over Mrs Clinton due to her victories in some big states such as California and New York.

On the Republican side, front-runner John McCain won Wisconsin to confirm his strong lead over party rival Mike Huckabee.

Meanwhile in Hawaii, Obama supporters distributed information ahead of the state's caucus, which began later on Tuesday.