President Donald Trump has claimed he is the only thing standing between "democracy and the mob", as he lashed out at protesters who accosted his supporters as they left the White House the night before.

Sowing fear about the implications of a Joe Biden victory in the forthcoming presidential election to battleground state voters, Mr Trump held a rally in New Hampshire on Friday.

Fresh from accepting the Republican nomination to seek re-election, Mr Trump is looking to close his Democratic rival's lead with just over two months until polling day by launching an aggressive travel schedule - and continuing to flout coronavirus guidelines.

Mr Trump opened his rally in Londonderry with a rant against demonstrators who confronted those leaving his Republican national convention speech on the South Lawn of the White House.

Some guests at the political event, including Kentucky senator Rand Paul, needed to be escorted by police officers to safety upon leaving the White House grounds.

"They walked out to a bunch of thugs," Mr Trump said, criticising District of Columbia Mayor Muriel Bowser for not doing more to protect his supporters.

"Unhinged, manic rage," he added. "You ought to see last night in Washington, it was a disgrace."

The speech marked his latest attempt to frame the general election as a dire choice between two futures for America - a theme he is expected to amplify on the campaign trail.

Mr Trump said he directed White House chief of staff Mark Meadows to study how to call in the National Guard to the nation's capital.

The US leader previously ordered federal troops to the District in May amid protests over the killing of George Floyd in the custody of Minneapolis police.

"We're not supposed to go in unless we call it an insurrection, and that's a big statement," Mr Trump said.

"But you know what we're going to do? ... We're going to have to look at it, because we're not going to let that happen to people that go to the White House to celebrate our country."

Mr Trump said the protesters were "anarchists", adding: "They're just looking for trouble. Has nothing to do with George Floyd. Has nothing to do with anything. They don't even know who George Floyd is.

"The agitators will go from rioting in the streets to running the halls of government," he added, saying voters needed to support him to "save democracy from the mob".

"No-one will be safe in Biden's America," he added.

Speaking in New Hampshire, a state he lost in 2016 by fewer than 2,000 votes and is a top target for him in 2020, Mr Trump repeated unfounded allegations that thousands of voters were transported into the state from neighbouring Massachusetts four years ago.

He also launched a new attack on Democratic vice presidential candidate Kamala Harris, speculating on the possibility that she could assume the presidency from the 78-year-old Mr Biden.

"You know, I want to see the first woman president also, but I don't want to see a woman president get into that position the way she'd do it, and she's not competent," Mr Trump said.

"She's not competent."

He suggested his own daughter, White House senior adviser Ivanka Trump, as a more suitable occupant for the Oval Office.

While the coronavirus kills 1,000 Americans each day, Mr Trump defied his own administration's pandemic guidelines on Thursday to speak for more than an hour to a tightly packed, largely mask-less crowd.