Trump claimed in a series of March 4 tweets that Obama wiretapped him at Trump Tower during the election. Neither Trump nor his administration have offered any proof of this conspiracy theory beyond right-wing media reports. Both the House and Senate Intelligence Committees say they have seen no evidence that backs up Trump's claim.
A German reporter asked Trump about his allegation on Friday during a joint press conference with Merkel at the White House.
"As far as wiretapping, I guess, by this past administration, at least we have something in common, perhaps," Trump said, to laughter in the room.
Merkel looked at Trump but seemed to make an effort not to laugh or smile.
In 2013, Merkel found out through leaks by former U.S. defense contractor Edward Snowden that the Obama administration had listened in on her cell phone calls.
On Thursday, White House press secretary Sean Spicer claimed that Obama had worked with British intelligence officers to conduct surveillance on Trump. His evidence was a report by Fox News legal analyst Andrew Napolitano. The White House reportedly apologized after British officials came out and disputed Spicer and Napolitano.
"We've made clear to the U.S. administration that these claims are ridiculous and should be ignored. We've received assurances that these allegations won't be repeated," said a spokesman for British Prime Minister Theresa May.
Trump tried to wash his hands of the matter on Friday, taking no responsibility for it.
"And just to finish your question, we said nothing," he told the reporter. "All we did was quote a certain very talented legal mind who was the one responsible for saying that on television. I didn't make an opinion on it. That was a statement made by a very talented lawyer on Fox. So you shouldn't be talking to me, you should be talking to Fox."
Fox News host Shep Smith said Friday that the network could not substantiate Napolitano's claims.
Earlier Friday, Rep. Tom Cole (R-Okla.) said he believes Trump owes Obama an apology. The White House, however, has continued to stand by the president's tweets.