We put concerns to the Chief Fire Officer, who wanted to reassure the public that planning for major incidents is their priority.
The fire service watchdog found it was good at responding to fires but said it had concerns over its "ability to keep people safe".
Her Majesty's Inspectorate of Constabulary and Fire & Rescue Service said it was unprepared to respond effectively to tackle new 'marauding terrorist' threat.
Lead inspector Andy Cook said: "Specifically, it requires improvement at preventing fires and other risks; protecting the public through fire regulation; and responding to major and multi-agency incidents.
"I note that the Manchester Arena Inquiry was taking place at the time of our inspection. The service’s staff have confidence in the new leadership team.
"The service now needs to make sure it is prepared to form part of a multi-agency response to any future terrorist incident.
What did the inspection find?
The extent to which the service is effective at keeping people safe and secure from fire and other risks requires improvement.
The extent to which the service is efficient at keeping people safe and secure from fire and other risks requires improvement.
The extent to which the service looks after its people is good.
Greater Manchester Fire and Rescue Service says many of the issues raised in the critical government inspection report have already been addressed.
GMFRS CFO Dave Russel said: "In October we submitted a business case and implementation plan with associated governance on creating a permanent MTA capability to the Inspectorate.
"In recent weeks we have made further progress following positive discussions with the Fire Brigades Union (FBU).
"While those discussions are ongoing, we are confident they will deliver a positive outcome that will significantly improve the Service’s capacity and capability to respond to a terrorist incident."
The report recognised the improvements that Greater Manchester Fire Service has made since the previous inspection in 2019.
The service is now rated 'good' at looking after its staff and promoting diversity in the workplace, which has improved from 'inadequate'.
Mr Russel continued: "Keeping the people of Greater Manchester safe is our most important job and the public should be reassured that the Inspectorate concludes that GMFRS is Good at ‘understanding fires and other risks’, Good at ‘responding to fires and other emergencies’ and has clear ‘arrangements in place to respond to major and multi-agency incidents’."
The Fire Brigade Union say the problems are stemmed from austerity under the Conservative government, describing it as a 'disaster' for the fire service.
Regional secretary for the North West, Ed Burrows said that: "Between 2010 and 2019 more than £20 million was removed from its budget, and since 2010 nearly one in three of Greater Manchester’s firefighters have been cut. That’s appalling."