The strikes killed at least 26 people, according to Reuters.
Cooper, Britain’s top diplomat, said that the ceasefire “must hold and humanitarian aid must get through to those in need.”
She urged that “all parties” uphold the ceasefire agreement to “avoid any further bloodshed.”
Speaking to reporters on Air Force One Sunday night, US President Donald Trump said the ceasefire in Gaza was still in effect, despite the deadly strikes.
Trump was unable to say if the Israeli strikes were justified: “I’d have to get back to you on that.”
The Hamas-run government media office in Gaza says Israel has killed 97 Palestinians and violated the ceasefire agreement 80 times since it went into force.