SAN FRANCISCO (NYTIMES, AFP) - Over the past few weeks, Mark Zuckerberg, Facebook's chief executive, and his lieutenants have watched the US presidential race with an increasing sense of alarm.

Executives have held meetings to discuss President Donald Trump's evasive comments about whether he would accept a peaceful transfer of power if he lost the election. They watched Trump tell the Proud Boys, a far-right group that has endorsed violence, to "stand back and stand by".

And they have had conversations with civil rights groups, who have privately told them that the company needs to do more because Election Day could erupt into chaos, Facebook employees said.

That has resulted in new actions.

On Wednesday (Oct 7), Facebook said it would take more preventive measures to keep political candidates from using it to manipulate the election's outcome and its aftermath.

The company now plans to prohibit all political and issue-based advertising after the polls close on Nov 3 for an undetermined length of time. And it said it would place notifications at the top of the News Feed notifying people that no winner had been decided until a victor was declared by news outlets.

"This is shaping up to be a very unique election," Guy Rosen, vice president for integrity at Facebook, said in a call with reporters on Wednesday.

Facebook is doing more to safeguard its platform after introducing measures to reduce election misinformation and interference on its site just last month. At the time, Facebook said it planned to ban new political ads for a contained period - the week before Election Day - and would act swiftly against posts that tried to dissuade people from voting.

Zuckerberg also said Facebook would not make any other changes until there was an official election result.

But the additional moves underscore the sense of emergency about the election, as the level of contentiousness has risen between Trump and his opponent, Joe Biden.

On Tuesday (Oct 6), to help blunt further political turmoil, Facebook also said it would remove any group, page or Instagram account that openly identified with QAnon, the pro-Trump conspiracy movement.

Policies against voter intimidation instituted by Facebook four years ago have been consistently expanded to account for new trends and tactics to intimidate or prevent voting, according to vice president of content policy Monika Bickert.

"As we head into the last days of this election, we know we will see spikes in efforts to intimidate voters," Bickert said at the briefing.

Wednesday's tightening of rules included barring posts that reference weapons or armies in encouraging people to monitor polling places on election day, according to Bickert.

"We will remove statements of intent or advocacy to go to an election site with military language," Bickert said.

"We will also remove calls to go to polls to monitor if it involves exerting control or showing power."

Facebook already banned posts directly urging people to go to polling places with weapons or to stop people from voting.