"You know what they say: As Ohio goes, so goes the nation. Well, this nation's coming back and so is this campaign," Clinton told roaring supporters after the Ohio projections were announced.
 
In the Republican race, John McCain has secured the party's nomination by gaining the necessary 1,191 delegates after wins in Vermont, Ohio, Rhode Island and Texas.
 
Clinton 'comeback'
 
The former first lady still faces a sizable deficit to Democratic rival Barack Obama in delegates for the August nominating convention.
 
Delegate breakdown

Democrats   Republicans
Clinton - 1,042   Huckabee - 248
Obama - 1,202   McCain - 1,205
Total needed: 2,025   Total needed: 1,191

Clinton beat out Obama 55 per cent to 43 per cent in Ohio, with a slimmer lead of 51 per cent to 47 per cent in Texas.
 
However, official results are not expected from Texas for some time as the southern state also holds Democratic caucuses after the primary vote.
 
Obama had earlier captured the state of Vermont, before his string of 12 straight wins was broken.
 
Shrugging off Tuesday's losses, Obama told supporters in San Antonio, Texas: "No matter what happens tonight, we have nearly the same delegate lead as we did this morning, and we are on our way to winning this nomination."
 
Turnout was heavy in all four states, and the Obama and Clinton campaigns traded accusations of irregularities at the polls in both Ohio and Texas.
 
Al Jazeera's Kimberly Halkett, reporting from Ohio, said turnout was considerable with more than 50 per cent of the state voting.
 
Some polling stations were kept open later because of poor weather, she added.
 
'Big battle' ahead
 
John
McCain's victory in the Republican nomination came a month after his success in multiple states on so-called "Super Tuesday" gave him a large lead in the delegate race and led to his main rival, former Massachusetts governor Mitt Romney, dropping out.
 
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At a speech in Dallas, Texas, McCain looked ahead to the presidential election and said "the big battle is to come".
 
"I do not underestimate the significance nor the size of the challenge," he said.
 
"I understand the responsibilities I incur with this nomination and I will not ... slight a single one."
 
He is expected to be formally endorsed by George Bush, the US president, later in the week.
 
His former rival, Mike Huckabee, also speaking in Texas, announced he was dropping out of the race and said he had spoken with McCain to congratulate him.
 
He also urged the Republican party to unite behind one candidate.
 
"It's now important that we turn our attention not to what could have been or what we wanted to have been but what now must be, and that is a united party," the former Arkansas governor told supporters.
 
McCain has made support for continuing the US war effort in Iraq a centrepiece of his campaign.
 
Rob Reynolds, Al Jazeera's correspondent in Dallas, Texas, said: "McCain can now move forward with fundraising efforts and with building a nationwide organisation oriented toward the general election campaign, while Hillary Clinton and Barack Obama are still fighting among themselves for the Democratic nomination.
 
"But McCain still has not completely won the hearts and minds of his partys conservative wing, which dislikes his stands on tax cuts, immigration and other issues."

Source: Agencies