U.S. President Barack Obama on Wednesday congratulated Mitt Romney for clinching the Republican presidential nomination, while their campaign teams attack each other in an increasingly relentless manner.

The two candidates for the 2012 presidential election "had a very good conversation," which was "friendly" but "not particularly long," White House Press Secretary Jay Carney said on a daily briefing.

During the telephone talk, Obama told Romney that he looked forward to "an important and healthy debate about America's future" between the two in the fall, Carney added.

The president also "wished (former Massachusetts) Governor Romney and his family well throughout the upcoming campaign," he said.

A campaign aide to Romney described the phone call as "brief and cordial."

Late Tuesday, Romney won the Texas primary with no surprise and surpassed the 1,144-delegate threshold he needed to claim the Republican nomination at the party's convention in August.

Since second-placed Republican candidate Rick Santorum dropped off in April, Romney has become the presumptive nominee for the Republican party, and the race between him and Obama has geared up.

William Galston, a U.S. politics expert and senior fellow with think tank Brookings, said job creation and economic recovery will be the master of Obama's fate on his re-election bid.

Both the incumbent's and the challenger's campaign teams have been warring over who would best lead the U.S. economy. Romney's campaign claims the successful private-sector background makes Romney much more suited to improve the economy than the incumbent president.

Obama's campaign argues that the Obama administration has improved the job creation and the economy recovery out of an "inherited burden" left behind be the former administration of George W. Bush.

The president's team also raised doubts over Romney's business background and even released a hard-hitting ad calling Bain Capital, a private equity firm formerly run by Romney, as a job-killing "vampire."

A Gallup survey released Wednesday showed Obama and Romney were currently tied in approvals on the presidential election trail.