Rick Santorum suspends campaign

Republican presidential candidate Rick Santorum has dropped his campaign, leaving former Massachusetts Governor Mitt Romney as the presumptive nominee.

The former Pennsylvania senator made the announcement at a news conference in Gettysburg in his home state.

"While this presidential race is over for me, we are not done fighting," he said.

The social conservative had been campaigning for Pennsylvania's primary on 24 April.

But he was far behind Mr Romney in terms of funding and the number of delegates needed to seal the nomination at the Republican convention in Tampa, Florida, in late August.

In a statement, Mr Romney congratulated him on his campaign, calling him an "able and worthy competitor".

"He has proven himself to be an important voice in our party and in the nation," the former Massachusetts governor said.

After recent losses in Wisconsin and Maryland, Mr Santorum had 285 delegates compared to Mr Romney's 661, according to an Associated Press tally.

Former House of Representatives Speaker Newt Gingrich and Texas Congressman Ron Paul remain in the race, but are even further behind Mr Romney.

The private equity multi-millionaire is viewed as the all but certain nominee who will face Democratic President Barack Obama in November's election.

Mr Santorum made the announcement with his wife and children standing behind him.

He proved to be the most resilient of the Republican rivals challenging Mr Romney's front-runner status. In his statement, he said he had surpassed expectations, competing "against all odds".

The former Pennsylvania senator made no specific mention of Mr Romney, although he reportedly telephoned the former governor to concede shortly before speaking to reporters.