Democratic presidential nominee Joe Biden on Sunday denounced the alleged harassment of one of his campaign buses by Donald Trump supporters on a Texas highway, in an incident the FBI confirmed it is investigating.

Video posted on Twitter appears to show multiple trucks waving Trump flags surrounding and slowing the Biden/Harris bus.

Democratic officials said the bus, carrying state congressional candidate Wendy Davis, stopped its journey and canceled two planned events and a news conference, citing "safety concerns."

The president himself tweeted a video of the incident late Saturday, saying, "I LOVE TEXAS."

"We've never had anything like this -- at least we've never had a president who thinks it's a good thing," Biden told supporters in Philadelphia.

He added that the president's son, Donald Trump Jr, made a video urging backers to "keep it up," and find where Biden running mate Kamala Harris is and greet her the same way.

"Folks, that's not who we are. We are so much better than this," Biden said.

The FBI's San Antonio office told AFP Sunday they were investigating the Texas incident but declined to give further comment.

An SUV belonging to the Democratic caravan was reportedly sideswiped. No injuries were reported, and it was unclear whether anyone involved was armed.

Biden campaign bus
Video posted on Twitter appears to show multiple trucks waving Donald Trump flags surrounding and slowing a Biden/Harris bus (similar to this one pictured February 2020) on a Texas highway Photo: GETTY IMAGES NORTH AMERICA / JOE RAEDLE

Meantime, multiple posts on Twitter showed scenes of long traffic backups on New Jersey's Garden State Parkway reportedly caused by pro-Trump drivers.

The reported incidents came amid high concern about voter suppression or intimidation, and post-election violence.

Amid the continuing fears, Democratic officials in Floyd County, Georgia, said Sunday they were canceling a campaign event after learning that a "large militia presence is expected" due to Trump's planned evening rally in the city of Rome, Georgia.

And during a rally in Michigan, Trump explicitly embraced the action, saying that the Texas protesters were trying to "protect" the Biden bus.

"You see the way our people, you know, they were protecting this bus yesterday," he said, adding that the Trump supporters numbered in the "hundreds."

The bus was separate from a visit to Texas on Friday by Harris, whose presence was seen to show that Democrats see a chance of flipping the traditionally conservative state.

"Rather than engage in productive conversation... Trump supporters in Texas (Friday) instead decided to put our staff, surrogates, supporters, and others in harm's way," Tariq Thowfeek, a Texas spokesman for the Biden campaign, told The Texas Tribune.

Local media said the incident occurred on the I-35 highway, southwest of Austin, the state capital.

The Texas Tribune quoted the state's Republican chairman, Allen West, as dismissing the incident as "fake news and propaganda," adding, "Stop bothering me."

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