In an interview with Sky News, Burnham says the issue of possible Iranian involvement in the suspected planned terrorist attack is "complicated" and that, due to an ongoing police investigation, he cannot comment further on the matter.
"We have been waiting to be able to substantiate what we say, but now we can confirm that we believe Iran played a role," he says.
Five men were arrested on Sunday on suspicion of planning a terrorist attack against RAF Fairford air base, which is used by both the UK and the US.
The men, all British citizens aged 20-25, were released on bail on Monday.
