Clinton 'coming back'
"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 in Columbus, Ohio.
|Clinton - 1,042
||Huckabee - 248|
|Obama - 1,202
||McCain - 1,205|
|Total needed: 2,025
||Total needed: 1,191|
Clinton led Democratic rival Barack Obama slightly, 51 per cent to 47 per cent, with about 77 per cent of the precincts counted 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.
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.
Clinton's Ohio win is seen to have breathed new life into her campaign and is almost certain to extend the heavily contested nomination on to Pennsylvania on April 22.
The former first lady, however, still faces a sizable deficit to Obama in delegates for the August nominating convention.
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."
'Big battle' ahead
McCain's victory comes one 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.
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.
Al Jazeera's correspondent Rob Reynolds in Dallas, Texas, said that the task ahead for McCain was to work out how to bridge the gap with the Republican party's social conservatives, who still viewed him with suspicion.