Democrat Joe Biden stands on the verge of winning the US presidency, as he expanded his narrow leads over President Donald Trump in the battleground states of Pennsylvania and Georgia three days after polls closed.

Mr Biden has a 253 to 214 lead in the state-by-state Electoral College vote that determines the winner, according to Edison Research. 

Winning Pennsylvania's 20 electoral votes would put the former vice president over the 270 he needs to secure the presidency.

Mr Biden would also win the election if he takes two of the three other key states where he held narrow leads: Georgia, Arizona and Nevada. 

Like Pennsylvania, all three are still processing ballots.

As he inches closer to triumph, Mr Biden is expected to address the nation later tonight, according to two people familiar with his plans. 

It may be a victory speech, given that his aides say Mr Biden appears on the cusp of winning.

Meanwhile, Mr Trump has showed little sign he is ready to concede, making clear in a statement he would continue to press his unsubstantiated claims of election fraud.

"From the beginning we have said that all legal ballots must be counted and all illegal ballots should not be counted, yet we have met resistance to this basic principle by Democrats at every turn," he said in a statement released by his campaign.

"We will pursue this process through every aspect of the law to guarantee that the American people have confidence in our government," Mr Trump said.

We need your consent to load this rte-player contentWe use rte-player to manage extra content that can set cookies on your device and collect data about your activity. Please review their details and accept them to load the content.Manage Preferences

Full results from 2020 US Election
Who leads in US states still counting?

The statement came a day after Mr Trump leveled an extraordinary attack on the democratic process by a sitting president, appearing at the White House yesterday evening to falsely claim the election was being "stolen" from him.

In both Pennsylvania and Georgia, Mr Biden overtook Mr Trump as officials processed thousands of mail-in ballots that were cast in urban Democratic strongholds including Philadelphia and Atlanta.

The surge in mail voting has slowed the counting process in numerous states, a fresh reminder of the pandemic that will remain the next president's most formidable challenge.

Hundreds of Democrats gathered outside Philadelphia's downtown vote-counting site, wearing yellow shirts reading "Count Every Vote." 

In Detroit, a crowd of Trump supporters, some armed, protested outside the counting location, waving flags and chanting, "Fight!"

A sense of grim resignation has settled in at the White House, where the president was monitoring TV and talking to advisers on the phone.

One adviser said it was clear the race was tilting against Mr Trump, but that the President was not ready to admit defeat.

His campaign is pursuing a series of lawsuits across battleground states, but legal experts described them as unlikely to succeed in altering the election outcome.

The campaign's general counsel, Matt Morgan, asserted in a statement that the elections in Georgia, Nevada and Pennsylvania all suffered from improprieties and that Mr Trump would eventually prevail in Arizona.

He also said the campaign expected to pursue a recount in Georgia, as it has said it will do in Wisconsin, where Mr Biden won by more than 20,000 votes. 

A margin that wide has never been overturned by a recount, according to Edison Research.

Election officials across the nation have said they are unaware of any significant irregularities. 

Georgia officials said they expect a recount, which can be requested by a candidate if the final margin is less than 0.5%, as it currently is.

Mr Biden expressed confidence yesterday that he would win and urged patience.

In response to the idea that Mr Trump might not concede, Biden spokesman Andrew Bates said in a statement: "The United States government is perfectly capable of escorting trespassers out of the White House."

The close election has underscored the nation's deep political divides, and if he wins Biden will face a difficult task governing in a deeply polarised Washington.

Republicans could keep control of the US Senate pending the outcome of four undecided Senate races, including two in Georgia, and they would likely block large parts of his legislative agenda, including expanding healthcare and fighting climate change.

The presidential winner will confront a pandemic that has killed more than 235,000 people in the United States and left millions more out of work, and a country grappling with the aftermath of months of unrest over racism and police brutality.

In Pennsylvania, Mr Biden moved ahead of Mr Trump for the first time and had a lead of 13,371 votes by midday local time, while in Georgia, he was 1,579 votes ahead. 

Both margins were expected to grow as additional ballots were tallied. 

Pennsylvania officials estimated they had 40,000 ballots left to count, while Georgia officials said this morning there were around 4,000 regular ballots remaining.

Mr Biden, 77, would be the first Democrat to win Georgia since fellow Democrat Bill Clinton in 1992.

In Arizona, Mr Biden's lead grew slightly to 43,779 votes, and in Nevada his margin jumped to 20,552.

Pennsylvania, one of three traditionally Democratic states along with Michigan and Wisconsin that handed Mr Trump his 2016 victory, had long been seen as crucial to the 2020 race, and both candidates lavished enormous sums of money and time on the state.

Mr Trump, 74, has sought to portray as fraudulent the slow counting of mail-in ballots, which surged in popularity due to fears of exposure to the coronavirus through in-person voting.

States have historically taken time after Election Day totally all votes, although in most presidential elections the gap between candidates has been big enough that television networks project the winner before counting formally ends.