WASHINGTON (Reuters) —Workers installed a fence around the U.S. Capitol late on Wednesday ahead of a protest scheduled for Sept. 18, and police asked the National Guard to be ready to help with security if needed.

A large group is expected at the Capitol on Saturday to protest the arrests and criminal charges against some 600 people in connection with a Jan. 6 riot by supporters of former President Donald Trump.

The tall fence was first erected following the Jan. 6 attack on the building that houses the U.S. Senate and House of Representatives. It was dismantled in July.

The U.S. Capitol Police on Wednesday said it has asked the Pentagon to provide National Guard troops if they are needed to help with security.

“The USCP has asked the Department of Defense for the ability to receive National Guard support should the need arise on September 18,” the police department statement said.

No details were provided on the potential number of National Guard troops that could be deployed.

Trump falsely claimed that the election was stolen from him as a result of massive election fraud. He gave a fiery speech to supporters at a rally on Jan. 6 outside the White House just prior to their attack on the Capitol.

Battling law enforcement outside and inside the Capitol, the rioters were trying to stop Congress from formal certification of Joe Biden’s victory in the November 2020 presidential election.

Many of the Jan. 6 rioters carried Trump flags, which at times were used as weapons against law enforcement.

Four people died on the day of the riot, one fatally shot by police and three from medical emergencies. A Capitol Police officer who had been attacked by protesters died the following day. Four police officers who took part in the defense of the Capitol later committed suicide.

Reporting by Richard Cowan; additional reporting by Jonathan Ernst Editing by Chris Reese, Bill Berkrot and Lincoln Feast.