It is perverse that these individuals ... would seek to capitalise on the events of the last days and weeks to further their own extremist agenda

Gloria Feldt, Planned Parenthood Federation of America

Gloria Feldt, president of Planned Parenthood Federation of America (PPFA), said: "It is perverse that these individuals here at home, who are themselves terrorists by virtue of their actions, would seek to capitalise on the events of the last days and weeks to further their own extremist agenda."

She said even if the letters were a hoax, these were "intolerable acts of terror", and called for every effort to be made to apprehend the perpetrators.

Message

Planned Parenthood said some of the letters included messages from the Army of God, a hard-line anti-abortion group.

These envelopes had a pre-printed return address for the US Marshall's Office and the Secret Service.

Some had an embossed message that said "Time sensitive - urgent security notice - open immediately".

Ann Glazier, security director for the PPFA, told the Boston Globe newspaper the organisation was used to receiving letters purporting to contain anthrax.

The organisation received 26 such letters in 1998 and 18 letters in 1999 purporting to be laced with anthrax.

Security procedures

Employees in Planned Parenthood offices who open mail have security procedures, such as wearing rubber gloves.

Jennifer Vriens, director of the Elizabeth Blackwell Health Center for Women in Philadelphia, told US National Public Radio's 'Morning Edition': "When the mail came, I put on latex gloves and took the mail to an empty room and gingerly went through the mail and found, indeed, one of these letters that we were warned we might receive.

"I isolated the letter, I put it in a bag and called 911."

She added: "All clinics across the country have all sorts of protocols related to bomb threats, phone threats, mail threats, physical threats ... we have protocols for all of these types of potential events."

On the same radio station, Donald Spitz, head of Pro-Life Virginia said he supported the action of the person who had sent the letters.

But Vicki Saporta, head of the National Abortion Federation said: "While we're certainly hoping that these are hoaxes and that none of our members' lives or health are at risk, it really is despicable for anti-choice extremists to be taking advantage of the country's angst."