Gaza's Hamas rulers on Monday said the condition of one of the Israelis it is holding captive has deteriorated.
The announcement marked a rare piece of information about the Israelis in Hamas captivity. The movement has given no details on the conditions or whereabouts of its prisoners, and it has never allowed the Red Cross to visit them.
There was no immediate comment from Israel.
Hamas is believed to be holding the remains of two soldiers killed during a 2014 war. Israel has pronounced the soldiers dead, though Hamas has never confirmed this.
In addition, Hamas is believed to be holding two Israeli civilians who wandered across the frontier into Gaza.
It has demanded the release of hundreds of Palestinian prisoners, including people convicted in deadly attacks, in exchange for the captive Israelis.
Abu Obeida, a spokesman for Hamas' armed wing, announced "a deterioration in the health of one of the enemy prisoners." He said more details were expected to be released later Monday.
Israel and Hamas are bitter enemies that have fought four wars and dozens of smaller skirmishes since Hamas seized control of Gaza 15 years ago.
Israel and Egypt have maintained a tight blockade over the territory throughout that time. Israel says the closure is needed to prevent Hamas from building up its military capabilities, while critics say the policy amounts to collective punishment.
Israel says there can be no major moves toward lifting the blockade until the soldiers' remains and captive civilians are released.