United States defence officials say 3,000 more American troops are being sent to the Middle East as Iran vows revenge for the death of one of its top generals.
Iran confirmed the death of General Qassem Soleimani, who was the commander of the Islamic Revolutionary Guard Corps.
The Pentagon said President Donald Trump ordered the killing of General Soleimani in an airstrike, claiming he was "actively developing plans to attack American diplomats and service members in Iraq and throughout the region".
Officials say the reinforcements are from the 82nd Airborne Division, based at Fort Bragg, North Carolina.
Prior to this week's deployments, 14,000 extra soldiers had already been sent from the US to the Middle East since May.
The UK is reviewing its "force protection" in the region, following General Soleimani's death.
Around 400 British Army personnel are deployed in Iraq, across three bases - Camp Taji near Baghdad, Union III in Baghdad, and Erbil in Iraqi Kurdistan.
The UK also has six Royal Navy ships in the Gulf - Type 45 destroyer HMS Defender, Type 23 frigate HMS Montrose and four minehunters.
Cover image: Protestors hold aloft a placard vowing revenge for the death of General Qassem Soleimani.