CNN: A woman walked slowly toward the door of the abortion clinic when a nearby protester screamed, "Don't kill your baby!"

But the shouts on this day were drowned out by women's rights groups who gathered at the Abortion & Contraception Clinic of Nebraska in Bellevue, just south of Omaha.

"Welcome! Welcome! This clinic stays open," abortion supporters chanted in unison, their voices rising every time anti-abortion activists tried to shout at patients arriving at the clinic.

Anti-abortion groups, led by Operation Rescue, and supporters of abortion rights rallied Saturday outside the clinic operated by LeRoy Carhart, one of the nation's few remaining doctors who perform late-term abortions. Carhart was best friends with George Tiller, one of the world's most well-known doctors performing abortions.

Tiller was shot in the head at point-blank range on May 31 as services began at Reformation Lutheran Church in Wichita, Kansas. Scott Roeder, a 51-year-old anti-abortion activist, is charged in Tiller's killing. He has pleaded not guilty.

The rally in Bellevue came nearly three months to the day after Tiller's killing. A massive police presence, including heavily armed rapid-response teams, monitored the demonstrators. Streets were blocked off, and police kept both sides separated with buffer zones in between.

Abortion rights supporters outnumbered their opponents nearly 2 to 1.

Operation Rescue drove in two of their so-called Truth Trucks, delivery trucks with giant billboards of dismembered fetuses on the sides. The vehicles parked in a designated area outside the clinic to gasps from the women's rights groups. Police used sniffer dogs to make sure the vehicles did not have any explosives before allowing them to park.

Megan Belleavia called the trucks abortion "pornography" that shouldn't be allowed. "You can't stand out in the street corner and show pictures of a bare-breasted woman without getting in trouble, so why should they be able to show that?" she said.

About 50 anti-abortion demonstrators prayed near the trucks, asking God to forgive what was happening inside the clinic. One woman held a sign that said, " I like to listen to my Mommy's voice." About 10 people stood with red tape over their mouths, with the word "Life" written across it.

Mike Whitaker said the tape symbolized "the silent cry that the babies have when they're actually being killed in there."

As he spoke, about a dozen abortion-rights supporters stood on the clinic property, their backs to those who oppose abortions. "A woman has a right to choose," they sang.

"A lot of towns will have things that stick out, positive things. This is something that's really a negative, a huge negative, for the city to have an abortion clinic here," said Whitaker, a 30-year resident of Bellevue.

Whitaker said he comes nearly every Saturday to pray for Carhart and those inside.

Larry Donlan of Rescue the Heartland said, "What we're doing today is what we do every day that this killing center is open. We're here to give assistance to mothers and pray for the dead and the wounded," Donlan said.

In all, about 100 women's rights supporters were on hand, spread out over the clinic property and near its entrance. Dozens gathered along a main street holding signs that read "Dr. Carhart is a hero" and "Keep abortion legal." When passing cars honked at them, they responded with loud hurrahs.

Michelle Fadeley drove from the Chicago area to support Carhart. "Someone who is willing to put his own life on the line to save thousands of other women's lives is truly a hero," said Fadeley, who works for a local Illinois chapter of the National Organization for Women.

Anthony Hardwick of Omaha clutched a sign that read "Women are not an incubator."

"What it means to me is that women are not solely for the purpose of procreation. They're not little vessels for men to plant their seeds in," he said.

Supporters of women's rights groups spread the word ahead of Saturday's demonstration that Operation Rescue was coming to protest outside Carhart's clinic. In the wake of the killing of Tiller, they said they wanted to show up in large numbers; supporters from at least 16 states were present Saturday.

Troy Newman, the president of Operation Rescue, was unfazed by it all. He has pledged to try to shut down Carhart's clinic.

Operation Rescue and other anti-abortion groups have asked Nebraska Attorney General Jon Bruning to investigate the clinic, alleging it has "an unacceptable safety risk to women."

Bruning has referred the matter to the state Department of Health and Human Services. A spokeswoman for the health department would only say they're looking into the matter and that Carhart's clinic has been in compliance with the law in previous inspections over the last decade.

"This is the beginning, not the end," Newman said outside the clinic. "All these NOW women will go home tomorrow, but we're going to be embedded here in the community."

Inside, Carhart continued to perform abortions.

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