Dulles (United States) (AFP) - US security authorities organizing Donald Trump's inauguration as president next week plan tough barriers against the kinds of jihadist-inspired truck attacks that left dozens dead last year in France and Germany.

Homeland Security Secretary Jeh Johnson said Friday the government sees no immediate threats for the January 20 inauguration, during which close to a million people could amass in downtown Washington.

Johnson said US authorities have ramped up security preparations in light of the rise of "lone wolf" type attacks, including recent atrocities in Nice, France and Berlin, Germany in which attackers drove trucks into large crowds.

But he stressed: "We know of no specific credible threat" to the massive event.

Addressing reporters at a secure communications facility west of the capital where dozens of US agencies will coordinate security for the quadrennial event, Johnson said 700,000-900,000 people are expected, including 99 different protest groups.

Some 28,000 security officials will be deployed.

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"The global terrorist environment is very different even from 2013" when President Barack Obama was inaugurated for his second term, said Johnson.

"We have to be concerned about home-grown violent extremism, home-born violent extremism, acts of self-radicalization."

"Aside from that, there is the larger picture of just general public safety when you have a large public gathering such as this."

Johnson said that with the two truck attacks in Europe in mind, the area for the inauguration ceremony and parade will be even more heavily cordoned off than four years ago.

It "will be more heavily fortified against unauthorized vehicles" using heavy trucks, dump trucks and trucks with cement.

On July 14, 86 people celebrating Bastille Day in the French seaside resort of Nice were killed when a Tunisian extremist reportedly inspired by the radical Islamic State group drove a truck through a crowd.

Five months later, on December 19, another Tunisian man ploughed a tractor-trailer into a Christmas market in Berlin, killing 12 people; Islamic State later claimed responsibility.