The United States carried out strikes against two Iran-linked sites in Syria on Sunday in response to attacks on American forces, Defense Secretary Lloyd Austin said.

It is the third time in less than three weeks that the US military has targeted locations in Syria it said were tied to Iran, which supports various armed groups that Washington blames for a spike in attacks on its forces in the Middle East.

"US military forces conducted precision strikes today on facilities in eastern Syria used by Iran's Islamic Revolutionary Guard Corps (IRGC) and Iran-affiliated groups in response to continued attacks against US personnel in Iraq and Syria," Austin said in a statement. 

"The strikes were conducted against a training facility and a safe house near the cities of Albu Kamal and Mayadeen, respectively," he said.

The United States targeted a Tehran-linked weapons storage site in Syria on Wednesday and also hit two facilities in the country on 26 October that it said were used by Iran and affiliated organizations.

Washington assesses that none of the previous strikes resulted in casualties.

The United States says the strikes are aimed at deterring attacks on American forces in Iraq and Syria — more than 45 since October 17 — that have wounded dozens of US personnel.

The surge in attacks on US troops in recent weeks is linked to the war between Israel and Hamas, which began when the Palestinian militant group carried out a shock cross-border attack from Gaza on October 7 that Israeli officials say killed about 1,200 people.

Israel's military responded with a relentless air, land, and naval assault on Gaza that the territory's health ministry said has killed more than 11,100 people — deaths that have sparked widespread anger in the Middle East, and criticism against Washington from Iran-backed groups.

There are roughly 2,500 American troops in Iraq and some 900 in Syria as part of efforts to prevent a resurgence of the Islamic State group.

The jihadists once held significant territory in both countries but were pushed back by local ground forces supported by international air strikes in a bloody, multi-year conflict.

The Gaza conflict has had repercussions for the United States outside of Iraq and Syria, with the Iran-backed Huthi rebels in Yemen saying Wednesday that they shot down a US drone that was "carrying out hostile surveillance and espionage activities in Yemeni territorial waters as part of American military support" for Israel.

Senior officials from the United States — which rushed military support to Israel and also bolstered American forces in the region after the 7 October attack — have confirmed that one of the country's drones was downed.