The probe is led by the Terror Financing unit of the US Treasury Department, part of a broad US effort to prevent Western-made goods from ending up in the hands of the terror group.
Toyota's Hilux pickups and Land Cruiser SUVs are often seen in the terrorist group's propaganda videos, prompting US counter-terrorism officials to open a probe into how the vehicles were obtained, US news broadcaster ABC News reported.
When IS soldiers paraded through the centre of Raqqa in Syria, more than two-thirds of the vehicles were Toyotas with the black emblems of the terrorist groups, the report said.
In a statement, Toyota, the world's second largest auto maker, said today that it is cooperating with the US government's investigation into how the Islamic State (IS) is obtaining its trucks and sports utility vehicles.
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"We are supporting the US Treasury Department's broader inquiry into international supply chains and the flow of capital and goods in the Middle East," Toyota spokesperson Amanda Rice said.
Toyota's own figures show sales of Hilux and Land Cruisers tripling from 6,000 sold in Iraq in 2011 to 18,000 sold in 2013, before sales dropped back to 13,000 in 2014.
The company said it is not aware of any dealership selling to the terror group but "would immediately" take action if it did, including termination of the distribution agreement.