Image caption Cruz said he had never taken "affirmative steps" to claim Canadian citizenship

A firebrand conservative Republican US senator born in Canada has vowed to renounce Canadian citizenship.

Ted Cruz of Texas, a possible 2016 presidential contender, said he had "nothing against Canada".

Born to an American mother and Cuban father, he moved to the US aged four and grew up identifying as American.

The US constitution states only a "natural born citizen" is eligible for the presidency, though no-one has challenged whether Mr Cruz could serve.

Mr Cruz, 42, acted after a Dallas newspaper reported at the weekend his birth in the western Canadian city of Calgary conferred dual US-Canadian citizenship.

The Harvard-trained lawyer and former Supreme Court law clerk was elected to the US Senate in 2012 and has quickly risen to prominence with his bombastic rhetoric, most of it directed toward President Barack Obama, his policies, appointees and fellow Democrats.

'American by birth'

At the weekend, Mr Cruz released a copy of his birth certificate to the Dallas Morning News, in what some analysts are describing as a move to stave off eventual questions about his eligibility for the White House.

The facts of my birth are straightforward Senator Ted Cruz

The US constitution offers no guidance as to what confers "natural born" citizenship, although there is near universal agreement the term refers at minimum to those born on US soil.

During the 2008 presidential election, the US Congress passed legislation clarifying that Senator John McCain, Mr Obama's Republican opponent, who was born to a naval officer in the Panama Canal Zone, was eligible for the presidency.

There has been no serious public debate about whether Mr Cruz would be eligible for the presidency.

Some analysts see the public discussion of Mr Cruz's birth and citizenship as particularly ironic given that some in the so-called "birther" faction on the American right have spent years attempting to tar Mr Obama as foreign-born and thus ineligible for the White House.

Mr Obama's father was Kenyan and the president spent much of his childhood in Indonesia. Mr Obama was born in Hawaii, a US state, and is thus a natural born US citizen.

Late on Monday, Mr Cruz said: "The facts of my birth are straightforward."

"Because my mother was a US citizen, born in Delaware, I was a US citizen by birth," he said in a statement. "When I was a kid, my Mom told me that I could choose to claim Canadian citizenship if I wanted. I got my US passport in high school."

He said he had never taken "affirmative steps" to claim Canadian citizenship.

But now, "I will renounce any Canadian citizenship. Nothing against Canada, but I'm an American by birth and as a US Senator, I believe I should be only an American.''