Romney eyes Illinois primary after Puerto Rico win
US Republican presidential candidate Mitt Romney is campaigning hard in the crucial primary state of Illinois after his easy weekend win in Puerto Rico.
The former Massachusetts governor secured 83% of the vote in Puerto Rico with 83% of the ballot counted.
His nearest rival for the candidacy, social conservative Rick Santorum, won barely 8%.
Meanwhile, President Obama's campaign has raised $45m (£28.4m) for his re-election bid in February.
Mr Romney's campaign is pulling out all the stops in the mid-western state of Illinois after he lost the Mississippi and Alabama primaries to Mr Santorum last week.
A candidate needs to accumulate 1,144 delegates to the Republican National Convention in August in order to secure the nomination.
With Puerto Rico's result, Mr Romney has 521 delegates. Mr Santorum has 253 delegates, former House Speaker Newt Gingrich has 136 and Ron Paul had 50, according to an Associated Press tally.
A new pollsuggests Mr Romney has a convincing lead in Illinois, leading Mr Santorum by 15 points among likely Republican voters in the state.
Mr Romney's well-financed campaign and its allies have already spent $2.5m in adverts in the state.
He is using the Puerto Rico win to call on the other Republican candidates to quit the nomination race.
Ann Romney told supporters in Illinois on Sunday that Republican voters "need to send a message that it's time to coalesce".
"It's time to get behind one candidate and get the job done so we can move on to the next challenge, bringing us one step closer to defeating Barack Obama," she said with her husband standing next to her.
But while acknowledging he is lagging in the battle for delegates, Mr Santorum has vowed to continue campaigning, citing tepid support for Mr Romney, even in states the former Massachusetts governor has won.
On Monday, Mr Santorum, a former Pennsylvania senator, said he would "go out and compete in every state".
"I think it's going to be very difficult as this goes on for anybody to get that magic number," Mr Santorum said in an interview with CBS News, adding that chances were increasing of the nomination being decided at the convention.
Mr Romney has turned to attacking Mr Obama in advance of the Illinois primary, calling him an "economic lightweight".
Mr Romney, speaking at a town hall meeting in the mid-western state, described the Puerto Rico result as an "extraordinary victory".
"Those people who don't think Latinos will vote for a Republican need to take a look at Puerto Rico," he said.
Some observers thought Mr Santorum, a devout Catholic and opponent of abortion and gay marriage, might do well in the predominantly Roman Catholic territory.
But he angered many last week when he suggested Puerto Rico needed to make English its official language if it wanted to become the US's 51st state.
The 3.7 million inhabitants of the Spanish-speaking Caribbean island - which is currently a self-governing US commonwealth territory - will vote in November in a statehood referendum.
Because it is not a state, Puerto Ricans can choose party candidates, but will not be able to vote in the 6 November presidential election.