Six Israeli hostages released in the Gaza Strip returned to Israel late Thursday, the Israeli prime minister's office said, hours before a truce extension was due to expire.

The release of the six -- four adults, a 17-old girl and an 18-year-old man -- who mediator Qatar said included Uruguayan, Mexican and Russian dual nationals, came after two women, including a French-Israeli dual national, were released earlier in the day.

That brought the total freed on Thursday to eight, while the truce agreement stipulates that a minimum of 10 Israeli hostages should be released alive each day.

The discrepancy came as mediators pursued discussions to extend the truce, which was due to expire at 0500 GMT on Friday.

A source close to Hamas told AFP that it considered two Russian-Israeli women released on Wednesday in addition to the required 10 as part of the seventh group freed, so that "as a result, the number of (hostages) in the seventh group is 10".

Mediator Qatar appeared to back the calculation.

The agreement requires Israel to release three Palestinian prisoners for every hostage freed, and Qatari foreign ministry spokesman Majed Al Ansari said 30 Palestinians would be released from Israeli prisons, in exchange for a total of 10 hostages, a tally which included "two Russian citizens who were released yesterday".

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