Former US president Barack Obama has denied wire-tapping Donald Trump during the 2016 election.
Trump claimed in a tweet that he was spied on by the former president during his election campaign and that Trump Tower had been bugged.
Trump tweeted: "How low has President Obama gone to tapp my phones during the very sacred election process. This is Nixon/Watergate. Bad (or sick) guy!
"I'd bet a good lawyer could make a great case out of the fact that President Obama was tapping my phones in October, just prior to Election!"
But a spokesman for Obama denied Trump's claims, which he tweeted without any evidence to support his claims.
Obama spokesman Kevin Lewis said in a statement seen by Reuters: "Neither President Obama nor any White House official ever ordered surveillance on any U.S. citizen. Any suggestion otherwise is simply false."
He added: "A cardinal rule of the Obama Administration was that no White House official ever interfered with any independent investigation led by the Department of Justice."
It is not clear where Trump's claims came from, but Lewis' statement has raised the possibility Trump may have been the subject of an investigation by the Justice Department, which could have ordered a wiretap.
However, there has been no evidence given to suggest this possibility, and Obama's people have strongly denied any involvement by the former president, if indeed there had been an instance of wiretapping.
Obama's former adviser Ben Rhodes took to Twitter, stating: "No president can order a wiretap. Those restrictions were put in place to protect citizens from people like you."