The United States have said that "very serious" negotiations were taking place on a new ceasefire in the Gaza Strip and release of more Israeli hostages, but prospects for a deal remained uncertain with Hamas insisting that it would not discuss anything less than a complete end to Israel's offensive in the Palestinian enclave.

Hamas leader Ismail Haniyeh visited Egypt on Wednesday for the first time in more than a month for discussions with Egyptian officials who are seeking to mediate another truce.

A source briefed on the negotiations said envoys were intensively discussing which of the hostages still held by Palestinian Islamist militants in Gaza could be freed in a new truce and which Palestinian prisoners Israel might release in return.