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President Donald Trump used a joint press conference with German Chancellor Angela Merkel to deflect criticism about his unsubstantiated claim that the Obama administration spied on him, reviving a sensitive diplomatic incident in which the U.S. was revealed to have snooped on her cell phone.

"At least we have something in common, perhaps," Trump said in response to a question from a German reporter, referencing a secret program revealed by National Security Agency leaker Edward Snowden.

The comment reflected the tension that permeated the joint press conference.

Merkel opened by making an apparent dig at the new American president even as the two look to repair what has been a strained relationship during their meeting Friday in Washington.

“It’s much much better to talk to one another than about one another,” Merkel said, perhaps referencing a number of comments Trump made about her during the campaign trail.

Trump's fourth joint press conference with a foreign leader, which followed the meeting, was also one of his most tense after Trump and Merkel clashed over major policy differences and the basic role of their countries in the world.

Trump once called Merkel "probably the greatest leader in the world," but used her as a foil during his presidential campaign to represent the cosmopolitan globalism he campaigned against.

While Trump called himself "Mr. Brexit," Merkel, as the longtime leader of the continent's most powerful country, is the European Union's staunchest defender.

While Trump has called for banning refugees, Merkel touted Germany's willingness to accept them and a spokesman said the chancellor had to "explain" international refugee law to Trump when the two spoke by phone shortly after his inauguration.

While Trump has cast doubt on the need for NATO and global action to address climate change, Merkel has been an outspoken advocate of both. And while Trump has called for warmer relations with Russian President Vladimir Putin, Merkel has been far more circumspect.

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And as Merkel tries to fend off the rise of the populist far-right in Europe, leaders of that movement are citing Trump's victory as inspiration.

But they sought to paper over past slights and present a more or less united front.

“Our two nations share much in common, including our desire for prosperity, security, and peace,” Trump said.

Both the White House and Germany chancellery cast optimistic notes heading into the meeting, saying it was an important opportunity for leaders of two of the world's most powerful democracies to come together.

But even behind closed doors, tension remained.

In a closed-door meeting before the press conference, Trump had pressed Merkel to increase funding for NATO and she announced that she had agreed to increase her country’s defense spending to 2 percent of Gross Domestic Product by 2024.

Trump has questioned the relevance of NATO and said other countries need to contribute more.

“These nations must pay what they owe,” he said Friday.

But while committing to increase defense funding, Merkel also said diplomacy and development are important elements of security — just as Trump’s White House seeks deep cuts to both areas to pay for a military buildup.

She also referenced the success of the Marshall Plan, the massive American investment in Europe’s rebuilding after World War II.

While major policy accomplishments were not expected, the meeting could help warm relations ahead of the G20 summit in Hamburg in July and a G7 meeting in May.

In the final question of the press conference, Trump was asked about his wiretapping claims, which have dominated news in the U.S. and strained relations with another ally, the United Kingdom, which Trump accused of aiding Obama’s alleged spying.

Instead of defending his claim, however, Trump passed responsibility onto a Fox News analyst who reported the alleged U.K. involvement, citing unnamed sources.

“We said nothing. All we did is quote a certain very talented legal mind. I didn’t make an opinion on it,” Trump told a German reporter.

The president added that if the reporter had further questions, he should ask Fox News, not Trump.

Fox News anchor Shepard Smith later Friday on air said Fox News has "no evidence" that Trump Tower was wiretapped, and cannot confirm the "commentary" of Fox News analyst Judge Andrew Napolitano.

"Fox News cannot confirm Judge Napolitano’s commentary. Fox News knows of no evidence of any kind that the now president of the United States was surveilled at any time, in any way," Smith said.

Shep: FOX News cannot confirm Judge Napolitano's commentary https://t.co/Y5Z8HT9rNm — Shepard Smith (@ShepNewsTeam) March 17, 2017

Trump also bristled at a question about why he labels press reports he dislikes as “fake news.”

“Nice friendly reporter,” Trump quipped.

Asked if he ever tweets things he regrets, Trump replied, “Very seldom.” Trump first made the wiretapping claims on Twitter.