WASHINGTON (BLOOMBERG) - Donald Trump is expected to issue a formal order drawing down US troops in Afghanistan and Iraq to 2,500 in each country by Jan 15, a US defence official said, as the president works to deliver on his longtime pledge to exit from "endless wars" in the Middle East.

US Central Command has received an informal warning order, according to the official. The expected order, reported earlier Monday by CNN, would reduce troops from about 4,500 in Afghanistan and from about 3,000 in Iraq before Trump leaves office.

Trump's deadline would come five days before President-elect Joe Biden takes office. Pentagon officials didn't immediately comment when asked about the drawdown.

The move comes after Trump fired Defence Secretary Mark Esper and replaced other top officials at the Pentagon with loyalists last week.

Esper sent a classified memo to the White House this month expressing concerns about additional troop cuts, the Washington Post has reported, citing two senior officials it didn't identify.

The reduced troop level for Afghanistan is consistent with public statements last month by National Security Adviser Robert O'Brien, although it stops short of a tweet by Trump expressing hope that US troops there would be home by Christmas.

Pressuring Taleban

Until now, US officials have maintained that the drawdown of forces in Afghanistan must be "conditions-based," in order to maintain pressure for Taliban forces to reach a peace accord with the Afghan government.

Chris Miller, a former Green Beret and White House counterterrorism coordinator who Trump chose as acting defense secretary, said in a memo to all Defence Department employees that "ending wars requires compromise and partnership."

"We met the challenge; we gave it our all," Miller said in the memo, reported earlier by McClatchy news. "Now, it's time to come home."

In Iraq, a reduction from about 5,200 troops was announced in September.

In January, Iraq's parliament had voted to expel American forces amid the uproar after the US killed Qassem Soleimani, an Iranian general who oversaw his country's foreign military operations, at Baghdad's airport.