Planned Parenthood, the US women's health care provider perennially attacked by conservatives, filed a lawsuit Thursday against an anti-abortion group it says filmed it illegally.

The conservative Center for Medical Progress last year released video it secretly filmed, purporting to show Planned Parenthood officials haggling over the sale price for aborted human fetuses.

The decades-old women's health network -- an important source of primary medical care for millions of American women over the years --  announced on its website that it has filed suit in US federal court against the Center for Medical Progress for filming their conversations without their consent or knowledge.

"For months, Planned Parenthood has faced false accusations, beginning with a series of illegally recorded and dishonestly edited videos," the group said in a fundraising letter on its site.

"This coordinated series of attacks was orchestrated by the Center for Medical Progress --  a front group for anti-abortion extremists who are hell-bent on shutting down Planned Parenthood and obstructing women's access to abortion.

"In their single-minded drive to attack Planned Parenthood, they lied, they broke the law, and they put health care access for millions of Americans at risk. Now, we're taking them to court to hold them accountable."

In the secretly-filmed video, officials from the conservative group pose as medical researchers interested in buying fetal tissue.

Planned Parenthood admits to having fallen prey to the ruse, but says its doctors were merely explaining the process of how fetal tissue is collected and distributed -- never sold, it insists -- for research purposes.

While strongly denying allegations that it sells human fetuses, Planned Parenthood nevertheless in October stopped accepting reimbursement for the costs associated with harvesting fetal tissue for research.

Planned Parenthood operates some 700 clinics across the United States providing a full complement of medical services for women, including birth control and abortions, as well as general health screenings.