At least 153 singing, chanting anti-abortion protesters were arrested Saturday after they began blocking an intersection near a medical center in Chicago in a demonstration timed to coincide with Mother's Day.

Another 84 arrests were made in a similar protest in Pittsburgh, authorities said.The Chicago protest was led by a group known as Chicago Rescue, which has blockaded abortion clinics in the past. The group denies affiliation with Operation Rescue, a nationwide anti-abortion organization that has engaged in civil disobedience resulting in mass arrests in Atlanta and other cities.

"Right now, we've got about 103 of them in here," said a desk officer at the Rogers Park District station, where many of those arrested were taken. Another 50 arrests were logged at the neighboring Belmont District station.

The anti-abortion activity was timed to coincide with Mother's Day, Chicago Rescue spokesmen said. Jay Huddle, a leader of the group, said the object of the protest was to prevent abortions.

The arrests began after anti-abortion protesters were prevented from marching in front of the clinic's doors and knelt down at an intersection near the Park Medical Center, authorities said. No injuries were reported.

Police counted about 50 counter-demonstrators. The two groups engaged in a brief shouting match, but police separated them and no violence was reported.

Trudy McCarthy, a spokeswoman for the Illinois Campaign for Choice, which escorts women seeking to enter clinics during anti-abortion protests, said Park Medical Center had 22 appointments scheduled for Saturday and only one was rescheduled.

Demostrators numbering a dozen or less, including pro-choice activists, also gathered at five other Chicago area locations.

Elsewhere, some 84 members of the anti-abortion group Operation Rescue were arrested in Pittsburgh Saturday during a demonstration outside a building that houses a clinic that performs abortions.