WASHINGTON (REUTERS) - The nation's capital on Friday (Jan 15) continued to boost security by shutting down access to iconic landmarks and erecting vehicle checkpoints at a security perimeter surrounding central Washington ahead of President-Elect Joe Biden's inauguration on Jan 20.

Presidential inaugurations are always tightly secure events with operations led by the US Secret Service, but this year's measures have been amped up after Trump supporters stormed the Capitol on Jan 6 in a bid to prevent the final certification of Biden's victory.

Law enforcement officials have warned of threats and armed groups in all 50 states.

The National Park Service said Friday it was immediately closing the National Mall and iconic US landmarks in Washington to visitors through at least Jan 21.

The Mall includes landmarks like the Lincoln Memorial and Washington Monument.

The area around the White House has also been closed, as has a key bridge over the Potomac River that connects Virginia to Washington, as well as East and West Potomac Parks, including Hains Point, which are near the Mall.

"We cannot allow a recurrence of the chaos and illegal activity that the United States and the world witnessed last week," Matthew Miller, the head of the Secret Service's Washington field office, told reporters.

Ken Cuccinelli, the acting deputy secretary of the US Department of Homeland Security, told CNN that Biden's team had decided to delay the inauguration rehearsal by one day due to "some of the online chatter talks about Sunday the 17th."

Still, Biden's chief of staff Ron Klain said in an interview with the Washington Post he was confident that law enforcement officials would be able to secure the inauguration.

A US official said the number of National Guard troops is expected to rise to 25,000 in Washington, DC, though an official request by local officials take some time.

At least 10,000 are expected to be in Washington by Saturday.

In downtown DC, Metropolitan AME Church, a historic black church that has hosted historical black luminaries like educator Booker T. Washington and journalist Ida B. Wells, said it has security plans in place but declined to provide details.

"We recognise that some people may be emboldened to focus on communities which have always prioritised justice, so we are cautious of that," a church official said.

Even before the Jan 6 siege, the inauguration was expected to be significantly different than previous swearing-in of presidents due to coronavirus concerns. Many of the events that accompany the ceremony will be virtual.

"This is not a concession to the terrorists. It is a recognition of the danger of Covid," US House Speaker Nancy Pelosi told reporters on Friday.