UPDATED: 07/18/2011 1:20 p.m.

CHICAGO (CBS) — St. Rita of Cascia High School on the city’s Southwest Side was placed on lockdown Monday morning, over concerns that an armed intruder may have been inside.

The school, at 7740 S. Western Ave., was placed on lockdown around 10:30 a.m., because of the armed intruder that may have entered earlier in the morning, according to an administrative assistant.

The lockdown was lifted early in the afternoon.

The administrative assistant said no one has been injured.

She says summer school is in session, so there are students on the campus.

Police confirm they were sent to the scene and that they are looking for a man wanted in a possible burglary from earlier this morning.

Police say the man is believed to be armed with a handgun – and was last seen heading toward St. Rita. Police say it is not known whether he was inside the school as of noontime.

Canine units are on the scene, police say.

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