The heads of the U.S. Central Intelligence Agency (CIA) and Israel's Mossad met Qatar's prime minister in Doha on Tuesday to build on the two-day extension of a truce between Israel and the Palestinian resistance group Hamas, a source briefed on the visit said.

The meeting was "to build on the progress of the extended humanitarian pause agreement and to initiate further discussions about the next phase of a potential deal," the source told Reuters.

The outcome of the talks, which were also attended by Egyptian officials, was unclear, the source added.

David Barnea, head of Israel's Mossad intelligence service, CIA Director William Burns and Qatari Prime Minister Sheikh Mohammed Bin Abdulrahman Al Thani met one day after Qatar announced the two-day extension of an original four-day truce deal in Gaza that had been due to expire overnight.

Qatar, where several political leaders of Hamas are based, has been leading negotiations between the Palestinian group and Israel.

Barnea and Burns were previously in Qatar to meet Sheikh Mohammed on Nov 9.

During the first four days of the truce, Hamas fighters released 50 Israeli women and children who had been taken hostage. In return, Israel released 150 security detainees from its jails, all women and teenagers.

As part of the two-day truce extension, Hamas has agreed to release an additional 10 Israeli women and children each day.

So far, there is no indication that Hamas is willing to release any Israeli men or military personnel among those taken captive.