The U.S. government might not be able to properly handle a nuclear terrorist attack or large-scale natural catastrophe, according to a Government Accountability Office report obtained by The Associated Press.

Congressional investigators found that the government "lacks effective coordination," and could be years away from having the capability to provide adequate emergency shelter and medical treatment, the AP said.

Even after it was embroiled in controversy following 2005's Hurricane Katrina and 2012's Superstorm Sandy, the federal agency responsible for dealing with emergencies, the U.S. Federal Emergency Management Agency (FEMA), failed to keep track of many disaster efforts by federal agencies, further hampering the nation's preparedness levels.

According to previously undisclosed documents, the Homeland Security Department highlighted how FEMA's 2013 disaster plan was in need of improvements before it could adequately deal with a nuclear attack.

"FEMA is not aware of the full range of information," and it could take one to five years to develop a strategy capable of measuring whether people were exposed to unsafe levels of radiation, the report noted, according to the AP.

An additional five to 10 years is needed to plan for a full medical response, with guidance also needed among first responders and medical shelters. FEMA is responsible for coordinating an interagency disaster response plan, and investigators advised FEMA to establish firm deadlines and a budget to ensure agencies meet goals.

When it comes to natural catastrophes, FEMA also needs to step up and take a bigger responsibility in coordinating an interagency response by establishing standards and collecting status reports, the report said.

The Energy Department was blamed for not effectively coordinating with state and private sector agencies during Superstorm Sandy, which resulted in at least 182 deaths and $65 billion in damages. Of the 102 corrective actions identified by federal agencies after Superstorm Sandy, 39 remain incomplete, said the GAO.

In response to the GAO report, Jim Crumpacker of Homeland Security said FEMA "will continue to coordinate and collaborate with other federal departments and agencies," and will have the recommendations in place by June, but said it did not have the legal authority to ask other agencies to act on the recommendations.