Aetna is sharply cutting its participation in Obamacare exchanges for 2017.

The health insurer said it will offer individual Affordable Care Act exchange plans in just four states, down from 15 this year, in an effort to reduce its losses.

"As a strong supporter of public exchanges as a means to meet the needs of the uninsured, we regret having to make this decision," Chairman and CEO Marc Bertolini said in a statement.

The insurance giant says it will offer ACA exchange plans in Delaware, Iowa, Nebraska and Virginia, slashing its Obamacare footprint by 70 percent next year. It will offer ACA plans in just 242 counties nationally, down from nearly 780 this year.

Aetna's announcement comes two weeks after the company booked $200 million in ACA-related pretax losses in its Q2 earnings report and nearly one month after the Department of Justice's antitrust division sued to block the health insurer's acquisition of rival Humana.

Humana has also announced it will sharply cut back from the exchanges. Its pullback, in the wake of UnitedHealth's departure from all but a handful of exchanges, means that hundreds of thousands of Obamacare plan members will no longer have access to plans from the nation's three major insurers in 2017.

Aetna has been one of the largest Obamacare players since the launch of the exchanges two years ago, offering plans in more than two dozen states. The Obama administration's chief executive of the federal marketplace attributed the insurer's departure to the forces of competition in an evolving insurance market.

"Aetna's decision to alter its Marketplace participation does not change the fundamental fact that the Health Insurance Marketplace will continue to bring quality coverage to millions of Americans next year and every year after that," Kevin Counihan, federal ACA marketplace CEO, said in a statement.

Officials at the Department of Health and Human Services note that as recently as April, Aetna's Bertolini had expressed strong support for the exchanges, telling analysts that it would have cost the company more than a $1 billion to acquire the million new customers it had signed up on Obamacare exchanges.