Baghdad, Iraq - A powerful Iraqi armed group told its fighters to prepare for the scenario of a long war in neighboring Iran should the President Donald Trump launch an attack.

Kataeb Hezbollah warned the US on Thursday of "immense losses" were it to start a war in the region, while a commander in an armed faction told AFP his group was "highly likely" to intervene in case of strikes.

"Amid American threats and military build-up indicating a dangerous escalation in the region, it is necessary" for all fighters "to prepare for a potentially long war of attrition," Kataeb Hezbollah said in a statement.

The commander told AFP that his group sees Iran as strategic to its own interests, and therefore any attack on the Islamic republic "directly threatens us."

US-sanctioned Iraqi armed groups did not intervene during the 12-day war between Israel and Iran last year.

This time, the commander said they would be "less restrained", especially in the event of strikes seeking to overthrow the regime.

For months during Israel's destruction of Gaza, groups allied with Iran carried out attacks against US troops in the region and mostly failed attempts against Israel.

Under mounting US and domestic pressure, these attacks came to a halt, while pressure on the groups to disarm has grown.

Iran-backed groups are part of the Axis of Resistance, which also includes Lebanon's Hezbollah, Hamas in Gaza, and the Houthis in Yemen.

A Hezbollah official told AFP this week that the Lebanese movement would not intervene militarily in the event of "limited" US strikes on Iran, but would consider any attack against supreme leader Ayatollah Ali Khamenei a "red line".

President Donald Trump has deployed warships and fighter jets near Iran to back up his threats of war should ongoing negotiations over Iran's nuclear and ballistic missile program fail.

US and Iranian negotiators met for a third round of talks on Thursday, with Iranian Foreign Minister Abbas Araghchi telling state TV that the talks "made very good progress."