WASHINGTONPresident Donald Trump refused Friday to back off his unsubstantiated accusation that President Barack Obama ordered surveillance of him, instead dismissing questions about it by cracking a joke that revived one of the most troublesome diplomatic episodes of Obama’s tenure.

Asked twice about his claim during a news conference with German Chancellor Angela Merkel, Trump ignored the first question and, only briefly addressed the issue in answering the second.

“As far as wiretapping, I guess, by this past administration, at least we have something in common, perhaps,” he said, gesturing toward Merkel and prompting an awkward smile from the German leader at an adjacent lectern.

Trump was referring to a disclosure in 2013 by former National Security Agency contractor Edward Snowden that the U.S. had monitored Merkel’s cellphone. The revelation dealt a major blow to U.S.-German relations, damaging Merkel’s standing at home and requiring significant diplomatic effort from the U.S. to patch up the relationship.

Friday’s comments, in which Trump variously blamed reporters, a Fox News commentator and British officials for rousing the debate, added to what has become worldwide fallout from Trump’s allegations against Obama, made in a series of early-morning tweets March 4.

Despite rebuttals from top intelligence officials and members of his own party, Trump has refused to apologize or retract what amounts to an explosive allegation against his predecessor.

Republican leaders have grown visibly frustrated at having to answer questions about the claim, which the White House defended even after leaders of the House and Senate intelligence committees said this week that they have seen no evidence to substantiate it.

In reviving the sore point with Merkel, Trump risked upsetting a delicate relationship with an important partner, which was already frayed by insults Trump lobbed at her during the presidential campaign in which he said she was ruining Germany by accepting too many refugees.

Trump’s talks with Merkel aimed to represent a restart of their relationship, and their meetings at the White House included discussions on strengthening NATO, fighting the Islamic State group, the conflict in Afghanistan and resolving Ukraine’s conflict, all matters that require close cooperation between the U.S. and Germany.

Meanwhile, the wiretap controversy caused a separate rift with Great Britain.

The British were ruffled after press secretary Sean Spicer read from a series of news stories while mounting a lengthy and vigorous defense of Trump’s claims from the White House briefing room podium during Thursday’s televised briefing. One was an allegation from the Fox News commentator, Andrew Napolitano, that Obama had used British spies to snoop on Trump at his New York high-rise.

The allegations are “nonsense” and “should be ignored,” an official for Britain’s General Communications Headquarters, its secretive signals intelligence agency, said in a rare statement.

British media reported that Spicer and H.R. McMaster, Trump’s national security adviser, issued a formal apology. A White House official who declined to be named pushed back against that characterization. The official said that British Ambassador Kim Darroch and Mark Lyall Grant, the British national security adviser, “expressed their concerns to Sean Spicer and Gen. McMaster.”

“Mr. Spicer and Gen. McMaster both explained that he was simply pointing to public reports and not endorsing any specific story,” said the White House official.

Trump also brushed the issue aside Friday.

“That was a statement made by a very talented lawyer on Fox,” Trump said.

But even Fox News, the conservative network that Trump considers a media ally, was unwilling to stand behind the 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,” anchor Shepard Smith said.

In related news reported by The Washington Post, the House Intelligence Committee did not reveal on Friday night whether Justice Department documents substantiate Trump’s wiretapping claims.

Chairman Devin Nunes, R-Calif., released a statement late Friday that said his panel is “satisfied” that DOJ “has fully complied” with its request related to “possible surveillance.”

Associated Press contributed.

noah.bierman@latimes.com