The Trump administration is being challenged to reveal how many troops the US has in Afghanistan, Iraq and Syria – and to explain why it stopped publishing those figures more than two years ago.

The Just Security website and the Project on Government Oversight have filed requests under the Freedom of Information Act (Foia) for the number of military and civilian defence personnel assigned to the three countries since December 2017, when public records were stopped. They also requested “underlying documents that explain why the [defence department] withheld the numbers”.

“The United States Government and all its institutions represent and are accountable to the American people,” the former defence secretary Chuck Hagel wrote in support of the requests. “The public and those who serve and defend this country and their families are entitled to know where we are sending our service men and women, why, and the numbers. That’s democracy. The Government works for the people.”

Ryan Goodman, the co-editor of Just Security and a former Pentagon legal adviser said: “Providing this information would be a show of respect for the American public, who ultimately must decide what sacrifices our country should make in sending troops into war.”

The administration’s decision to stop publishing troop numbers ended a decade-long policy of transparency started in the George W Bush administration. In December 2017, the Pentagon’s defence manpower data centre published its quarterly report with blank spaces where troop numbers in combat zones would normally be. Corresponding figures for Iraq, Syria and Afghanistan were also stripped retroactively from the previously released September report.

The decision to remove the data from the Pentagon website was the initiative of former defence secretary James Mattis, according to retired army Lt General Thomas Spoehr.

“He became convinced the Department of Defence was revealing too much information publicly,” Spoehr, head of the center for national defense at the Heritage Foundation, said. “I could never find a written memo, but he essentially told all the services to clamp down on what they were releasing to the public.”

In the move to greater secrecy, Mattis drew support from the president. In August 2017, Trump said in a speech in Virginia. “We will not talk about numbers of troops or our plans for further military activities … America’s enemies must never know our plans, or believe they can wait us out.”

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Goodman said such reasoning was contradictory. “I think the public justification has crystallized around the idea of operational security – ‘we don’t want to tell the enemy’ – in part because it is such an easy, off-the-shelf explanation to present,” he said. “But that makes no sense given the long period in which the military has released these numbers to the public without hesitation.”

Spoehr argued that Mattis had gone too far in withdrawing information from the public domain, but argued for a compromise in which approximate figures were disclosed, and with greater secrecy for Syrian operations, which tend to be more covert.

Troop numbers are also politically sensitive, particularly in an election year, as Trump has made his vows to bring US troops home from Afghanistan and the Middle East one of the central planks to his campaign message.

“Of all the things that DoD has done to limit public access to information, this is probably the most egregious,” said Steven Aftergood, director of the Federation of American Scientists government secrecy project. “The idea that the scale of the US military presence in a war zone should be kept secret from the public is a mistake. That’s not how democracies fight or win wars.”