US election 2016: Trump momentum forces new Clinton effort
As opinion polls suggest Donald Trump is gaining support, Hillary Clinton has been holding rallies in states that had been considered safe for the Democrats.
A BBC correspondent says both teams are now concentrating more on getting their supporters to vote, rather than swaying those undecided.
Thirty-seven million early ballots have already been cast.
US authorities say they are assessing the credibility of information on a possible al-Qaeda terror attack.
New York, Texas and Virginia are believed to be the potential targets mentioned in connection with a possible attack before election day on Tuesday, but a police spokesman said the information "lacks specificity".
Officials say they regularly assess all possible threats before major events.
News of a possible attack came as both Mrs Clinton and Mr Trump made final pushes for support in battleground states across the US.
They both held rallies in Ohio and Pennsylvania on Friday, two states that may prove crucial on Tuesday.
Both candidates are due to campaign in Florida today. The state is seen as a key contest that could tip the election.
In Cleveland, Ohio, Mrs Clinton ended the day's campaigning at a concert, where she was joined by the singer Beyonce and her husband, rapper Jay Z.
"We have unfinished work to do, more barriers to break, and with your help, a glass ceiling to crack once and for all," Mrs Clinton said.
Addressing the crowd, Jay Z explained his support for Mrs Clinton. He said that though he did not have any "ill will" towards Mr Trump, the Republican's conversation was "divisive".
"That's not an evolved soul to me, so he cannot be my president. He cannot be our president," he said.
The free concert was part of a series of events put on by Mrs Clinton's campaign as she aims to encourage greater African-American participation in the election.
Mr Trump, meanwhile, told a crowd of supporters in New Hampshire that his rival wants a "550% increase" on Syrian refugees allowed into the US.
"Her plan would mean generations of terrorism, extremism, and radicalism spreading into our schools and communities," the Republican candidate said.