Striking Chicago Teachers Union members march west on Roosevelt Road in Chicago. AP

Union leaders representing Chicago's striking teachers said on Wednesday that they approved a tentative contract deal with the school district but that they would not to return to work until the mayor agrees to make up for instructional days lost during the 10-day walkout.

The announcement came as the Chicago Public Schools district, the third-largest in the United States, issued a separate statement saying the strike would continue, with classes canceled again, for an 11th straight school day on Thursday.

Chicago Teachers Union members and their supporters march to Roosevelt Road and Halsted Street in Chicago. AP

After huddling in private to review the tentative settlement for several hours, leaders of the Chicago Teachers Union emerged to call on rank-and-file members to rally on Thursday to press their demand for extending the school calendar to offset days missed during the strike. "We have a tentative agreement, but we do not have a return-to-work agreement. So we will be at City Hall at 10am to demand the mayor return our days," the union said on Twitter.

Mayor Lori Lightfoot did not immediately respond, but she planned to hold her own news conference late Wednesday.

Any settlement is ultimately subject to approval by the union's House of Delegates, a body consisting of 825 elected representatives from each of the city's schools and support staff classifications, before classes can resume for the district's 300,000 students.

Chicago Teachers Union President Jesse Sharkey speaks during a news conference in Chicago. AP

The district has said it was looking into whether it could make up more than eight school days lost during a strike, and the Chicago Board of Education would need to vote on adding any attendance days to the school calendar.

The walkout followed a wave of teacher strikes across the country over wages and education funding during the past two years, including a weeklong work stoppage in Los Angeles in January. African-Americans and Hispanics account for the majority of Chicago's public school enrollment.

As was the case in Los Angeles, the labor dispute in Chicago centered on pay as well as teacher demands for contract language to reduce class size and increase staffing levels for support professionals, including nurses and social workers.

Reuters