Retired Army Lt. Gen. Keith Kellogg called former National Security Adviser John Bolton 'an architect of failure' and said that he watched him lie to US President Donald Trump to nearly starting a military conflict in Iran.

Kellogg, the national security adviser to Vice President Mike Pence, spoke on Wednesday night at the Republican National Convention to endorse Trump for making 'the right choices when faced with difficult decisions'.

He took a veiled swipe at Bolton, using the title of the former national security adviser’s book, a scathing portrayal of Trump titled 'The Room Where It Happened', saying: "He was in the room when the decisions were made."

"(Bolton) is actually an architect of failure," the 76-year-year-old Kellogg said on Fox News Thursday, adding: "He had his own agenda. He pushed his own agenda, and when it didn’t work, he tried to basically stifle the discussion going forward or lie to the president of the United States."

"I was there when it happened. I saw him when he fabricated information and nearly caused us to commence military operations in Iran because of the loss of a drone that we knew he had incorrect information and he passed that incorrect information to the president. I saw him on several occasions do that," Kellogg said.

He added that Bolton single-handedly 'destroyed negotiations' to end the war in Afghanistan.

"So, is John Bolton a liar? Yeah, he is," Kellogg said.

A source close to John Bolton, the former White House national security adviser, said Bolton had a verbal altercation with the US president shortly before he was expelled from the White House.