WASHINGTON (Reuters) - Republican presidential candidate Ron Paul said on Monday he was scaling back his White House bid and will no longer campaign actively in states that have yet to hold primary elections.

Instead, Paul's campaign will concentrate on trying to add to its tally of delegates to the Republican National Convention in August by sending large groups of supporters to state conventions to elect themselves to delegate slots.

"Our campaign will continue to work in the state convention process. We will continue to take leadership positions, win delegates, and carry a strong message to the Republican National Convention that liberty is the way of the future," Paul said in a statement.

"Moving forward, however, we will no longer spend resources campaigning in primaries in states that have not yet voted," he added. "Doing so with any hope of success would take many tens of millions of dollars we simply do not have," Paul said.

He is the last main challenger to presumptive nominee Mitt Romney in the Republican race to confront President Barack Obama.

Paul has yet to win any of the state nominating contests. So far, He has only 99 delegates while Romney has 949, according to Real Clear Politics. A candidate needs 1,144 to win the nomination.

Paul urged his supporters to vote in upcoming elections, even though he would not actively campaign in the states that still must hold a nominating contest ahead of the party's convention before the November 6 presidential election.

The 76-year-old Texas congressman's message of sharply reducing the role of government, scrapping the Federal Reserve and ending the U.S. military presence overseas is unique to him. Many of his supporters have said they would not vote at all on Election Day if Paul were not the nominee.

Paul's statement said his campaign would explain details of its delegate strategy "in the coming days."