Federal investigators in the US wiretapped the phone lines of Michael Cohen, the longtime personal lawyer for President Donald Trump, according to broadcaster NBC.

Mr Cohen is under investigation for a payment he made to porn star Stormy Daniels, who alleged she had an affair with Mr Trump.

NBC reports that the tap was in place in weeks leading up to the raids on Mr Cohen's offices, hotel room, and home in April.

At least one phone call between a phone line associated with Mr Cohen and the White House was intercepted, a person with direct knowledge told the broadcaster.

This comes as it has been revealed Mr Trump reimbursed Mr Cohen for a US$130,000 (€108,468) payment used to keep Ms Daniels quiet before the 2016 election.

President Trump has previously insisted he was unaware of the hush money handed to the adult actress to buy her silence over their alleged affair.

In February, Mr Cohen talked publicly about making the payment - claiming he had used his own money.

On Thursday, President Trump took to Twitter and appeared to confirm Mr Cohen was reimbursed.

However, he insisted no campaign money was used and again denied the alleged affair.

Daniels claims she had sex with Mr Trump in 2006, months after his third wife gave birth to his youngest child.

Rudy Giuliani, a member of Mr Trump's legal team, told Fox News that Mr Trump's payment to Mr Cohen "is going to turn out to be perfectly legal" because "that money was not campaign money."

Asked if President Trump knew about the arrangement, Mr Giuliani said: "He didn't know about the specifics of it, as far as I know. But he did know about the general arrangement - that Michael would take care of things like this, like I take care of things like this for my clients.

"I don't burden them with every single thing that comes along. These are busy people."