Facebook has seen an increase in signals indicating potential future acts of violence associated with efforts to contest the result of the U.S. presidential election since the Capitol siege last week, a company spokeswoman told Reuters.

The spokeswoman, who asked not to be named for security reasons, said the storming of the U.S. Capitol by armed pro-Trump demonstrators appeared to be a galvanizing event, spawning efforts to organize gatherings across the country around President-elect Joe Biden's inauguration.

On Monday, Facebook banned content promoting the phrase "stop the steal," which has become a rallying cry at armed pro-Trump protests.

Operating Officer Sheryl Sandberg told Reuters Next this week that the social media giant will continue to take down posts that may incite violence.

SHERYL SANDBERG: "To this day we are working to find any single mention that might be new to us and making sure that we get it down as quickly as possible."

The Facebook spokeswoman in Wednesday's exclusive said alarming new signals Facebook tracked included digital flyers promoting the events, some of them featuring calls to arms or the insignia of militias or hate groups.

The FBI has warned of armed protests being planned for Washington and all 50 U.S. state capitals in the run-up to the inauguration... prompting extraordinary measures in the U.S. Capitol - and a strong show of force from the National Guard .

Violent rhetoric on online platforms had already ramped up in the weeks before the deadly attack on Congress, when lawmakers were forced to flee as the Capitol was mobbed by Trump loyalists.

After the unrest, tech companies took unprecedented steps to crack down on the baseless claims of election fraud that had spurred calls for violence.

Twitter and Facebook blocked Trump's accounts, while Amazon Web Services and the major mobile app stores cut off social media network Parler - which had been used as a tool by Trump loyalists to communicate ahead of last Wednesday's events.

Under pressure from civil rights groups, Alphabet's YouTube suspended Trump's channel for seven days.

Speaking at the Reuters Next conference on Wednesday, Alphabet CEO Sundar Pichai said YouTube is monitoring Trump's YouTube channel in line with its three-strike policy.

"So we've been removing, you know, thousands of videos, including videos from President Trump's channel, if we found them to be violative. And, you know, we have a clear, consistent policies."

After the seven-day suspension ends, Pichai said YouTube will take future action based on what videos the Trump account posts, and despite facing even internal calls at Google to ban Trump altogether, Pichai referred to Google as a "noisy democracy."