President Donald Trump has accused former President Barack Obama of “wire tapping” Trump Tower before the 2016 presidential election.

Trump made the claims in a series of tweets that he posted early Saturday morning, although he offered no evidence to back his allegations up.

“Terrible!” Trump posted in his first message. “Just found out that Obama had my ‘wires tapped’ in Trump Tower just before the victory. Nothing found. This is McCarthyism!”

Read Trump’s full set of tweets below:

Terrible! Just found out that Obama had my “wires tapped” in Trump Tower just before the victory. Nothing found. This is McCarthyism!

— Donald J. Trump (@realDonaldTrump) March 4, 2017

Is it legal for a sitting President to be “wire tapping” a race for president prior to an election? Turned down by court earlier. A NEW LOW!

— Donald J. Trump (@realDonaldTrump) March 4, 2017

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!

— Donald J. Trump (@realDonaldTrump) March 4, 2017

How low has President Obama gone to tapp my phones during the very sacred election process. This is Nixon/Watergate. Bad (or sick) guy!

— Donald J. Trump (@realDonaldTrump) March 4, 2017

It’s currently unclear whether Trump has any proof to substantiate the allegations or if he was referencing a classified briefing.

This is a developing story.