CIA Director John Brennan has announced one of the most significant overhauls of the U.S. spy agency in its history. The move is expected to bring about dramatic changes in the organization's management structure.

In a memo to the agency's staff, Brennan said that the changes were "driven by two fundamental shifts in the national security landscape.” They are an increasing array of complex issues facing policymakers in Washington, as well as the "unprecedented pace and impact of technological advancements," the document said.

The most significant change is the breakdown of the barrier between clandestine, or undercover, agents and intelligence analysts. The existing system, which saw a separation between field agents who gathered intelligence and the analysts who interpreted its significance, will be abolished. In its place, a system inspired by the U.S. military's system of “central commands” will be implemented.

This will result in the creation of 10 so-called “Mission Centers,” which will see both agents and analysts reporting to a centralized command structure for specific areas, including terrorism, weapons proliferation and the Middle East. Each Mission Center will be run by an agency assistant director. A small number of CIA departments currently operate without a division between agents and analysts, including the agency's counterterrorism center.

“I’ve never seen a time when we have been confronted with such an array of very challenging, complex and serious threats to our national security, and issues that we have to grapple with,” Brennan said, according to the New York Times.

The new structure is intended to enhance the accountability of commanders in specific areas of agency activity. Addressing reporters before the announcement this week, Brennan said that it was unsatisfactory that in many instances, there was no single person he could hold accountable for a spying mission in any given part of the world.

"There are a lot of areas that I would like to have better insight to, better information about, better access to," Brennan said, according to The Associated Press. "Safe havens, denied areas. Whether because we don't even have a diplomatic presence in a country, or because there are parts of countries that have been overrun and taken over by terrorist groups and others."

The changes are the result of inputs from a group of “outstanding” agency officers that Brennan asked to review the organization's people, processes and structure last September.