by Melissa Gruz and Biodun Iginla, BBC News Analysts, Washington

Donald Trump is preparing to address an Independence Day military parade event in Washington DC that he promises will be the "show of a lifetime".

Thousands of troops are being assembled at a red-, white- and blue-draped Lincoln Memorial to hear the first such speech by a president since 1951.

Armoured carriers and tanks are part of the "Salute to America" backdrop.

Opponents accuse him of politicising the holiday ahead of a re-election campaign and wasting taxpayer's money.

The Pentagon has not revealed the cost of the extravaganza, which many believe was inspired by Mr Trump's visit to the Bastille Day parade hosted by French President Emmanuel Macron.

Some reports say the National Park Service is diverting nearly $2.5m (£2m) to cover the cost.

What will happen?

As well as tanks, Mr Trump's 4 July celebration will also feature a military jet flyover and an extended fireworks show.

As the armoured vehicles were transported from a railyard in south-eastern Washington DC on Tuesday evening, military officials advised residents not to be alarmed.

The two 70-tonne Abrams tanks have to stay on a side road as they are too heavy for the memorial's surrounding areas.

Media caption"If Korea can have a military parade, why can't we?"

In a morning tweet, Mr Trump said the parade was "turning out to be one of the biggest celebrations in the history of our Country".

He will be keeping a keen eye on the turnout, given the arguments over the claimed attendance of his inauguration ceremony back in 2017.

A couple of hours before kick off there was heavy rain falling on the National Mall, which may not help. Thunderstorms could also affect the flyovers.

The event will be open to the public free of charge, apart from a ticketed area for VIPs in front of the memorial.

Image captionSupporters of President Donald Trump gather on the National Mall

Large numbers of Trump supporters wearing Make American Great Again hats - and opponents upset at the cost - have been descending on the capital.

Trump supporter Brandon Lawrence told Reuters: "I think what Trump's doing with the tanks, all the flyovers, I think it's great."

Critic Medea Benjamin said: "This is costing us millions and millions of dollars. We the taxpayers are paying for it, for Donald Trump to use our military as a prop."

The musical playlist includes the Star Wars theme and Hail to the Chief.

The speech is at 18:30 local time (22:30 GMT).

The event has been largely good-humoured so far, although there were scuffles outside the White House after a flag-burning protest.

Who's invited?

Mr Trump will be joined by a Pentagon delegation led by the highest-ranking US military officer, Chairman of the Joint Chiefs of Staff General Joseph Dunford.

But the service chiefs of the Army, Navy, Air Force and Marine Corps will not attend.

The defence department said in a statement it had received 5,000 tickets from the White House.

The White House has also distributed VIP tickets to major donors and political appointees, amid reported concerns that empty seats might be visible.

Mr Trump's re-election campaign sent out an email this week encouraging supporters to attend the event. But the Democratic National Committee has been given no tickets.

And the cost?

Mr Trump said in a tweet that the expense "will be very little compared to what it is worth".

Military flyovers alone cost tens of thousands of dollars per hour.

Mr Trump's plans for a military display on Veterans Day in November last year were dropped after defence officials said it would cost about $92m - more than three times the original estimate.

What have opponents said?

They see it as an inappropriately partisan display and a misuse of public funds.

Image captionBaby Trump must stay tied down as it has been refused permission to fly

US presidential contender Joe Biden and two other Democratic candidates marched instead in Iowa, which kicks off the nomination race in seven months' time.

Senator Bernie Sanders wrote on Twitter: "This is what authoritarians do: Donald Trump is taking $2.5 million away from our National Park Service to glorify himself with a spectacle of military tanks rolling through Washington."

Protesters have brought along an inflatable balloon depicting Mr Trump as a baby but have been denied permission to use helium to make it airborne.

Harry Truman was the last president to speak before a large crowd on the Washington Monument - in 1951.