LOS ANGELES (AP) — Planned Parenthood Federation of America defended its practices Thursday in a lengthy letter to congressional leaders and included a report by experts it hired who found undercover videos of officials discussing fetal tissue for research were heavily altered by anti-abortion activists.

The report supports the organization's claims that the secretly recorded videos were distorted to misrepresent conversations employees had with anti-abortion activists posing as biomedical company employees interested in buying fetal tissue, Planned Parenthood said.

The letter and report were the most detailed defense to date by Planned Parenthood, which has come under fire from conservatives since the California-based Center for Medical Progress began releasing a series of undercover videos last month.

"It's increasingly clear that this attack on Planned Parenthood is a fraud based on a web of lies and deception," Executive Vice President Dawn Laguens told reporters.

Four congressional committees are investigating Planned Parenthood's practices, and lawmakers unsuccessfully tried to strip the organization of federal funding.

Some conservatives are vowing to vote down must-pass legislation to fund the federal government this fall unless it strips money for the organization, raising the specter of a government shutdown over the issue.

A spokeswoman for House Speaker John Boehner, R-Ohio, said a letter from Planned Parenthood isn't going to satisfy Congress.

"House committees have been investigating all of the participants involved in these horrific practices and building a strong case," spokeswoman Emily Schillinger said. "The American people deserve the facts — not PR releases."

The videos that include graphic images of tissue, organs and even a tiny arm, showed Planned Parenthood officials discussing in a businesslike way how they provide aborted fetal organs for research and what they charge for tissue.

Planned Parenthood's president, Cecile Richards, previously apologized for the "tone and statements." But she defended the organization in her letter to Congress, saying it did nothing illegal and calling the videos a "smear" on its reputation.

The organization provides health services such as birth control, sexual-disease screening and abortions. Fewer than 1 percent of 700 affiliated clinics nationwide offer fetal tissue donation for medical research, the letter said.

At issue is a federal law that prohibits abortion providers from profiting from the sale of fetal tissue, inducing someone to have an abortion to provide the tissue, or altering the procedure in any way to harvest fetal tissue, which is used for a variety of medical research.

California clinics were reimbursed $45 to $60 to recoup their costs, which is legal. Washington donated the tissue to a university.

An Oregon affiliate provides placental tissue to a university, and clinics in Texas and Colorado have provided similar tissue over the past five years, but not fetal tissue, Planned Parenthood said.

The Center for Medical Progress claims the videos released so far show Planned Parenthood illegally sells and harvests organs.

The Texas attorney general launched an investigation after a Planned Parenthood representative in Houston was recorded in the videos.

California's attorney general, a Democrat running for U.S. Senate, is investigating whether the group that made the videos violated registration or reporting requirements, or broke any other state rules.

Several other states have found no wrongdoing by Planned Parenthood.

Planned Parenthood said forensic experts found more than 40 instances where the video was spliced. They also found conversations taken out of context to change the meaning of what was said, the organization said.

In one example highlighted, a Planned Parenthood official in Texas had discussed lab protocols to maintain tissue. But the video was manipulated through editing so it sounded like she was talking about altering abortion methods to help harvest organs, Laguens said.

Research firm Fusion GPS said experts it hired on behalf of Planned Parenthood found it was impossible to determine how much edits to the video distorted the meaning of the meetings. But it said the footage had no evidentiary value in an inquiry unless the original material was provided to investigators.

Glenn Simpson of Fusion GPS said the video work was "sloppy at best" and that transcripts provided by the center were inaccurate and erroneous.

The activist who secretly recorded the video said in a statement that editing out bathroom breaks or waiting periods didn't change the meaning of the dialogue.

"Planned Parenthood's desperate, 11th-hour attempt to pay their hand-picked 'experts' to distract from the crimes documented on video is a complete failure," the center's founder, David Daleiden, said in a statement. "Planned Parenthood's abortion providers are far more honest about the brutal reality of their work than the paid political consultants at the national office."

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Erica Werner in Washington contributed to this report.