The United States has bases in both Syria and Iraq. With Washington a key ally of Israel, the sites have faced almost daily attacks claimed by Iran-linked groups since outbreak of the war in Gaza.
There are about 900 US troops stationed in Syria and 2,500 in Iraq as part of a coalition of forces in the fight against Islamic State.
Between Oct 17 and Jan 17, at least 140 attacks by drones, rockets, mortars and short-range ballistic missiles on US and other coalition forces were recorded in both countries, according to a US defence official.
83 of these attacks were in Syria, but most have failed to hit their targets, according to the official, who reported no fatalities in Syria, and just one in Iraq.
The majority have been claimed by the Islamic Resistance in Iraq, a loose alliance of Iran-linked armed groups that oppose US support for Israel in the Gaza war.
The situation remains contained for now, however, as the United States and Iran are seeking to control the degree of violence and avoid a broader conflict.
“Both sides are certainly trying to manage the level of violence, but that’s where the similarities stop,” said Aron Lund from the Century International think tank.
“The United States would prefer to see no violence at all, but Iran and its allies… are deliberately raising the level of conflict.”
They are trying to force Washington, either by forcing it to be drawn into the type of conflict that it had hoped to avoid or engage with their demands to rein in Israel in Gaza, he said.