The complexity and international spread of AIG’s operations impeded regulatory oversight of the derivatives unit that helped bring down the insurer, according to former executives, analysts and regulators.

Three former chief executives of AIG, including Hank Greenberg, will testify in US Congress on Tuesday about the events that forced the government to de facto nationalise the company last month. They may face questions on AIG Financial Products, which specialised in writing derivatives insurance on mortgage-backed securities.