The ABC has increased security at all its major Australian offices after threatening phone calls were made to the broadcaster following a controversial appearance by former terrorist suspect Zaky Mallah on its Q&A program.

The tightened security comes after Prime Minister Tony Abbott on Thursday intensified his criticism of Monday night's episode of Q&A, saying inviting Mr Mallah on to the program was a "betrayal - if you like - of our country" and that "heads should roll" over that decision and the airing of a program repeat.

"There have been a number of threatening phone calls," a spokesman for the ABC said, confirming new security arrangements.