By Steve Holland and Emily Stephenson
MIAMI/WASHINGTON (Reuters) - Republican Donald Trump on Wednesday invited Russia to dig up tens of thousands of "missing" emails from Hillary Clinton's time at the U.S. State Department, vexing intelligence experts and prompting Democrats to accuse him of urging foreigners to spy on Americans.
"Russia, if you're listening, I hope you're able to find the 30,000 emails that are missing," Trump, the Republican presidential nominee, told reporters.
Trump made the remark at a testy news conference at his Doral golf resort in Florida that allowed him to steal some of the limelight from the Philadelphia convention where Clinton on Thursday will accept the Democratic presidential nomination for the Nov. 8 election.
The Clinton campaign shot back that Trump was posing a possible national security threat by encouraging a foreign power to conduct espionage in the United States. Some intelligence experts said the comments raised questions about Trump's judgment.
A spokesman for Trump, Jason Miller, tried to tamp down the storm of protest, saying Trump did not urge Russia to hack Clinton's emails.
Trump said on Twitter that if anyone had Clinton's emails, "perhaps they should share them with the FBI!"
The criticism of Trump's comments reverberated at the Democratic National Convention where speakers brought up the episode to try to intensify Democratic support for Clinton, who is running neck and neck with Trump in the polls.
"Donald Trump today once again took Russia’s side. He asked the Russians to interfere in American politics," longtime Clinton supporter and former CIA Director Leon Panetta said. "Donald Trump ... is asking one of our adversaries to engage in hacking or intelligence efforts against the United States of America to affect the election."
Another speaker, retired U.S. Rear Admiral John Hutson, said of Trump: "This morning, he personally invited Russia to hack us. That's not law and order, that's criminal intent."
Trump was referring in his remarks to a private email system Clinton kept while secretary of state from 2009 to 2013. She handed over thousands of emails in 2015 to U.S. officials probing that system, but did not release about 30,000 emails she said were personal and not work-related.
A Federal Bureau of Investigation probe of the issue found no basis for criminal charges, but FBI Director James Comey said this month there was evidence Clinton was "extremely careless" in her handling of classified information.
Trump dismissed suggestions that WikiLeaks' release of embarrassing Democratic Party emails last week was engineered by Russia to help nudge the U.S. election toward Trump, who has been called "very talented" by Russian President Vladimir Putin.
"It's just a total deflection, this whole thing with Russia," said Trump. "I never met Putin. I don't know who Putin is."
The Democratic Party chairwoman, Debbie Wasserman Schultz, resigned on Sunday after the leaked emails showed party leaders favoring Clinton over her rival, U.S. Senator Bernie Sanders, for the presidential nomination.
Cyber security experts and U.S. officials have said there was evidence that Russia engineered the release of the sensitive party emails in order to influence the presidential election.
Throughout a day of campaigning, Trump suggested the culprit could be China or even, as he said in Scranton, Pennsylvania, "a 400-pound person lying in bed.”
Russia has brushed aside suggestions it was involved. "I don't want to use four-letter words," Russian Foreign Minister Sergei Lavrov told reporters on Tuesday.
Trump has alarmed European allies and many U.S. national security experts with talk of forcing NATO nations to pay more for the U.S. security umbrella.
"By the way, if they don't pay, bye bye," he said in Toledo, Ohio, on Wednesday night.
He has praised Putin in the past and said this week that if elected, he would seek an alliance with Moscow to take on Islamic State militants.
But he sought to distance himself from Putin at his news conference, saying his closest interaction with Russia was selling a Florida home to a Russian for more than he paid for it.
A U.S. State Department spokesman declined to comment on Trump's remarks on Wednesday.
Trump's vice presidential running mate, Indiana Governor Mike Pence, took a different approach from the Republican nominee, saying he expected the FBI to get to the bottom of the matter.
"If it is Russia, and they are interfering in our elections, I can assure you both parties and the United States government will ensure there are serious consequences," Pence said in a statement.
During the news conference, which lasted more than an hour, Trump also called Barack Obama, a Democrat, the most "ignorant" president ever and said Vice President Joe Biden was not bright.
Asked if he would recognize Crimea as Russian territory, Trump said he would be "looking into that." Crimea has long been part of Ukraine, but Russia annexed it in 2014 after pro-Russian separatists and special forces took over the region. The U.S. government considers it still part of Ukraine.
(Additional reporting by Emily Stephenson in Washington; Editing by Howard Goller and Peter Cooney)