A two-day strike by University of California hospital workers ended on Thursday, with both sides claiming victory even though there was no resolution to a contract dispute involving staffing and pensions.

The University of California said the vast majority of union workers had crossed picket lines to work at hospitals in several areas of the state.

In a dueling statement, union officials insisted the overwhelming majority of workers had participated in the strike.

The strike formally ended at 4 a.m. after thousands of hospital pharmacists, nursing assistants, operating room assistants and other health care workers joined the walkout organized by the American Federation of State, County and Municipal Employees.

Dr. John Stobo, senior vice president of the University of California's Health Sciences and Services, said the strike caused problems for patients.

"Make no mistake about it — (the strike) was extremely disruptive to patient care," he said. "But the human costs were minimized by thousands of our employees who put their patients first."

Union spokesman Todd Stenhouse disagreed, saying the union's court-validated patient protection plan was responsible for a lack of disruption.

The union said a key issue in the labor dispute is dangerously low staffing levels. UC officials counter that the union is refusing to accept a new pension plan

Green-shirted picketers marched outside medical centers, prompting the postponement of dozens of surgeries for patients at facilities in San Diego, Orange, Los Angeles, Santa Monica, San Francisco and Sacramento.

About 450 union employees remained in critical jobs under court order.