Donald Trump has abruptly postponed plans to announce his vice-presidential running mate following the "horrible attack" in Nice that left scores dead.
The Republican White House hopeful had planned to hold his first event with his yet-to-be-named running mate this morning in New York, but announced the change of plans on Thursday evening on Twitter.
In light of the horrible attack in Nice, France, I have postponed tomorrow's news conference concerning my Vice Presidential announcement.— Donald J. Trump (@realDonaldTrump) July 14, 2016
The stunning announcement raised questions about the status of Mr Trump's selection process.
Indiana governor Mike Pence had emerged as a late favourite for the job, though Mr Trump said he had not finalised the pick and advisers warned he could change his mind.
"I haven't made my final, final decision," Mr Trump said on Fox News Channel.
He said that while his running-mate selection would "absolutely not" be changed by the France attack, he did not feel it was appropriate to hold a news conference in its aftermath.
In addition to Mr Pence, Mr Trump's vice-presidential shortlist included former House of Representatives speaker Newt Gingrich and New Jersey governor Chris Christie, according to people familiar with the candidate's thinking.
Soon after last night's attacks, Mr Gingrich called for the expulsion of any Muslim who believed in Sharia law from the US.
The former Georgia congressman told Fox News Channel's Hannity that the US "should frankly test every person here who is of a Muslim background, and if they believe in Sharia, they should be deported.
"Sharia is incompatible with Western civilisation".
Scores of people were killed in the French southern resort city when a lorry drove on to a pavement, ploughing through a crowd of Bastille Day revellers who had gathered to watch fireworks.
Mr Trump told Fox News that if he was elected president he would ask Congress for a declaration of war on the so-called 'Islamic State' group.
Another horrific attack, this time in Nice, France. Many dead and injured. When will we learn? It is only getting worse.— Donald J. Trump (@realDonaldTrump) July 14, 2016
My prayers and condolences to the victims and families of the terrible tragedy in Nice, France. We are with you in every way!— Donald J. Trump (@realDonaldTrump) July 15, 2016
Democrat rival Hillary Clinton, also appearing on Fox, said the US needed to "stand strongly" with France and strengthen alliances, including with Nato, to ferret out terrorism and prevent future attacks.
She said she would intensify efforts to put together a more effective coalition against terrorism.
After spending much of Thursday in Indianapolis, Mr Pence flew to New York late in the day. Indianapolis television station WTHR posted a video showing Mr Pence arriving at a private airport outside New York.
Mr Trump did not say when he planned to announce his running mate but he is up against a clock - the Republican convention kicks off in Cleveland, Ohio, on Monday.
Top party officials are already in Cleveland, grappling with a rules fight that could increase the odds of nationally-televised clashes at the convention.
Late on Thursday, a committee at the Republican National Convention defeated an effort by conservatives who want to let delegates vote for any presidential candidate they would like. Conservatives hoped that would lead to delegates blocking Mr Trump's nomination.
The convention and vice-presidential announcement give Mr Trump back-to-back opportunities to reassure Americans - as well as leaders within his own party - that he is prepared for the presidency.
Mr Pence, a staunch conservative who served six terms in Congress, is seen as a running mate who would have the backing of party leaders and ease some of their concerns about Mr Trump's political inexperience and volatile temperament.
He has influential allies in Mr Trump's inner circle. But some of Mr Trump's children, who have been closely advising their father, are said to favour different candidates.
Campaign chairman Paul Manafort was among those urging caution in assuming any decision, saying on Twitter that Mr Trump's choice "will be made in the near future".
The contenders have been vetted by a top Washington lawyer and all have spent time with Mr Trump in recent days.
But the final decision rests with the candidate, who is known for making decisions more on instinct than other factors - and for sometimes changing his mind.
Mr Trump was in California on Thursday for several fund raisers. His schedule put him at a distance from many of his closest advisers, including Mr Manafort and his three oldest children.
Mr Pence is running for re-election, but Indiana law prevents him from seeking two offices at once. He faces a Friday deadline to withdraw from the governor's race.