UN Secretary-General Antonio Guterres urged Hamas to continue with the planned release of hostages on Tuesday, a day after the Palestinian militant group announced its intention to halt the exchange.

“We must avoid at all costs the resumption of hostilities in Gaza that would lead to an immense tragedy,” he said in a statement.

Hamas on Monday announced it would stop releasing Israeli hostages until further notice over what it called Israeli violations of a ceasefire agreement in Gaza, raising the risk of reigniting the conflict.

Hamas was to release more Israeli hostages on Saturday in exchange for Palestinian prisoners and other Palestinians held in Israeli detention as had happened over the past three weeks.

An Israeli delegation returned from Doha for talks on the next phase of the Gaza ceasefire, Prime Minister Benjamin Netanyahu’s office said on Monday, amid growing doubts over the Egyptian and Qatari-brokered process to end the war in Gaza.

“Both sides must fully abide by their commitments in the ceasefire agreement and resume negotiations in Doha for the second phase”, Guterres added.

US President Donald Trump said on Monday that Hamas should release all hostages held by the militant group in Gaza by midday Saturday or he would propose cancelling the Israel-Hamas ceasefire and “let hell break out.”

Senior Hamas official Sami Abu Zuhri told Reuters on Tuesday that US President Donald Trump must remember that the only way to bring home Israeli prisoners is to respect the ceasefire between Israel and Hamas.