Iran's supreme leader Ayatollah Ali Khamenei has called on Iraq to demand US troops leave "as soon as possible", warning that Washington is plotting to remove the Iraqi government.

Officials signed a short-term agreement on Sunday to boost South Korea's contribution toward the upkeep of US troops on the peninsula, after a previous deal lapsed amid US President Donald Trump's call for the South to pay more.

Pushing back against Republican opposition, US President Donald Trump reaffirmed his determination to pull US troops out of "endless wars" in Syria and Afghanistan, in an interview that aired yesterday.

A bomb attack claimed by Islamic State killed US troops in northern Syria on Wednesday, weeks after President Donald Trump said the group was defeated there and he would pull out all American forces.

President Donald Trump appeared Monday to water down shock plans for an immediate pullout of US troops from Syria, even as he defiantly claimed his achievements in the conflict should make him a "national hero."

Turkish-backed Syrian forces have reinforced the area around the town of Manbij, a rebel spokesman said on Monday, as they prepare for a withdrawal of US troops following Washington's surprise decision to pull out of Syria.

US President Donald Trump has decided to pull about 7,000 troops from Afghanistan, a US official said Friday, but the Afghan presidency brushed off concerns the drawdown would affect security.

President Donald Trump agreed in a National Security Council meeting this week to keep US troops in Syria a little longer but wants them out relatively soon, a senior administration official said on Wednesday.

US President Donald Trump in August committed nearly 4,000 additional troops to Afghanistan as part of an open-ended campaign against Taliban insurgents who have made advances in recent years.

The Pentagon has yet to decide how many more US troops to send to Afghanistan as it is still drawing up a plan, Defense Secretary James Mattis said on Tuesday, after President Donald Trump committed the United States to an open-ended war there.

Armed US troops are on the ground near Marawi City in the southern Philippines, but are not involved in fighting Islamist militants who have held parts of the city for more than three weeks, a Philippines military spokesman said.

As many as three Afghan civilians were killed early on Monday morning when American troops opened fire after their vehicle struck a roadside bomb, an official in eastern Nangarhar province said.