US President Donald Trump said on Sunday the triumphal arch he plans to build near Washington would double as a "military complex" housing drones and snipers, making it the second major construction project he has sought to justify on national security grounds.

The move, which Trump said came at the military's request, echoed the national security rationale he has used to defend the roughly US$400 million ballroom complex being built on the site of the White House's former East Wing. He did not identify any specific threats.

The arch and ballroom are part of Trump's broader effort to remake the nation's capital, including the renovation of the Lincoln Memorial Reflecting Pool, the redevelopment of a golf course in East Potomac Park, and a push to add his name to the John F Kennedy Center for the Performing Arts.

The initiatives have drawn criticism from preservationists and others who argue they would alter some of Washington's most prominent historic landmarks.

In a social media post, Trump said that at the "strong request" of the military he had agreed to turn the planned 76-metre arch "into a top grade Military Complex/Triumphal Arch, to house, store, and have the rapid ability to use large numbers of drones, plus Snipers, on both the roof and plaza areas, and additionally have and hold large quantities of sniper ammunition in storage."

Trump did not elaborate on why such capabilities would be needed at the arch, modelled on Paris' Arc de Triomphe and sited near Arlington National Cemetery, just across the Potomac River from Washington. He has similarly recast the ballroom as a national security project, with plans for a drone facility, bomb shelters and other military installations intended to protect Washington.

Mark Cancian, a retired Marine colonel, said that while there was a stronger case for enhancing security at the White House, including expanding underground bunker facilities, the rationale for militarising the arch was harder to discern.

Cancian said the move appeared aimed at countering opposition to the monument, which is planned for a traffic circle just 1 mile from Joint Base Myer-Henderson Hall, an active Army installation, and 2 miles from the Pentagon.

"It looks like it's tacked on in order to strengthen the rationale for construction," Cancian, a senior adviser with the Defense and Security Department at the Center for Strategic and International Studies, a Washington-based think tank, told Reuters.

"There is this military facility long established with a variety of military capabilities one mile away. So why you need this one isn't clear."

Cancian also said that storing ammunition at the arch would create logistical challenges and questioned the value of positioning snipers there.

US District Judge Tanya Chutkan earlier this month ordered the Trump administration to give 48 hours' notice before engaging in any activity on the site of the arch, which Trump proposed to mark the nation's 250th anniversary.

Her ruling came a day after the Interior Department announced plans to move forward with work on the arch despite legal challenges and the lack of final approval from a government planning authority.

Aviation experts have raised safety concerns given its proximity to Reagan Washington National Airport while veterans have sued to block the arch, arguing it would destroy the carefully designed historic sightline between the Lincoln Memorial and Arlington National Cemetery. (Reuters)



Edited by Cecil Wong