Conservative US Senator Rand Paul announced Tuesday he is running for the Republican Party's nomination for the 2016 presidential race.

"I am running for president to return our country to the principles of liberty and limited government," Paul said on his campaign website.

Paul was to make a public announcement later in the day at a rally in Louisville, Kentucky, the state he has served as senator since 2011.

He follows Texan and fellow senator Ted Cruz, who launched his Republican candidacy two weeks ago with an appeal to the religious right.

Paul's campaigns have been marked by a modern social media outreach and a highly polished design aesthetic in his promotional materials.

While staunchly conservative, the 52-year-old son of former candidate Ron Paul portrays himself as a libertarian rebel against the party establishment.

The eventual Republican flag-bearer's main opponent is all but certain to be Democratic frontrunner and former first lady Hillary Clinton.

Clinton has not formally declared a run, but she is virtually unchallenged within her party as the candidate to replace President Barack Obama.