"The secretary-general condemns the loss of civilian lives, including those of children and women, which he considers unacceptable and must cease immediately," Farhan Haq, UN deputy spokesman, said in a statement.
Guterres is following with deep concern the current escalation of tensions in the Palestinian territories, Haq said, warning of the ongoing escalation and the risk of further loss of life.
According to the Palestinian Ministry of Health, at least 21 Palestinians have been killed and 64 injured in two days of Israeli air strikes on Gaza.
.@antonioguterres is following with deep concern the latest security developments in Gaza & the ongoing escalation & risk of further loss of life. He urges all parties concerned to exercise maximum restraint & work to stop hostilities immediately: https://t.co/HndbS22YbY
"The Secretary-General also condemns the indiscriminate firing of rockets from Gaza into Israel, which violates international humanitarian law and endangers both Palestinian and Israeli civilians," Haq also said.
"Israel must comply with its obligations under international humanitarian law, including the proportional use of force and taking all feasible precautions to spare civilians and civilian objects in the conduct of military operations," the spokesman added.
The Secretary-General urged all parties involved to exercise maximum restraint and work to end hostilities immediately.
The Gaza Ministry of Education has announced a decision to "maintain the suspension of working hours of all educational institutions, schools and kindergartens on Thursday, May 11." Through a statement, the ministry extended "its deepest condolences to the families of the martyrs."