Rick Santorum is suspending his campaign for the U.S. Republican presidential nomination, clearing a path for Mitt Romney to become the party's nominee.

The former Pennsylvania senator, who saw his profile and support for his shoestring-budget campaign surge in recent months to become Romney's main challenger, made the announcement Tuesday in his home state of Pennsylvania. It was two weeks before the GOP presidential primary there.

"While this presidential race is over for me and we will suspend our campaign effective today, we are not done fighting," he told reporters at a press conference in Gettysburg, surrounded by his wife and six of his seven children.

Santorum had already suspended campaign appearances last week to be with his ailing daughter, Bella, 3, who was born with a rare genetic disorder often fatal among children and spent the Easter weekend in hospital.

He said his daughter was doing "exceptionally well" and is back home, but the weekend of "prayer and thought" made him and his wife, Karen, reflect on "the role that we have as parents in her life and the rest of our family."

Improbable run ends

The announcement marked the end of what was initially viewed as improbable run for the Republican nomination by Santorum, a staunch social conservative who has repeatedly questioned the consistency of Romney's positions on issues such as abortion and contraception, as well as his suitability as a conservative candidate.

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Despite a severe financial disadvantage, Santorum won several high-profile state races and made life difficult in the primary campaign for the well-financed juggernaut of Romney, who has received the backing most of the party's establishment and senior figures.

"Against all odds, we won 11 states, millions of votes," said Santorum, who vowed to continue to push for the end of Democratic incumbent President Barack Obama's presidency and reversal of policies such as health-care legislation and government regulation of business.

"We are going to continue to fight for Americans who stood up and gave us the air under our wings that led us to accomplish things that no political expert would have expected."

Santorum faced an uphill in Pennsylvania against Romney, who blitzed the state's airwaves with ads criticizing his rival.

With Santorum's departure, Romney, a former Massachusetts governor and successful CEO, is all but certain to secure the Republican nomination and face Obama in November's presidential election.

He has a massive delegate lead over his two remaining rivals, Texas congressman Ron Paul and former House of Representatives speaker Newt Gingrich.

Paul and Gingrich have so far resisted growing calls for them to drop out of the race, with Gingrich again vowing Monday he would stay in the Republican race all the way to the national convention in August in Tampa.