Hamas gunmen have reportedly surrounded the stronghold of the group holding BBC journalist Alan Johnston.
According to a report by the Associated Press, members of the movement's militia have moved on to rooftops and taken up positions in the streets in the Gaza neighbourhood that is home to his captors, the Army of Islam.
Johnston has been held hostage by the Army of Islam, which is led by Gaza's Doghmush clan, for nearly four months.
Earlier a Palestinian civilian was killed in the area, a death Hamas blamed on Doghmush fighters.
The Hamas interior ministry spokesman, Khaled Abu Hilal, said security forces would not spare any efforts to free Johnston.
A radio station run by Hamas has also urged people with any information about him to call a freephone number.
Today's developments follow the arrest yesterday of Abu Khatab al-Maqdisi, a spokesman for the Army of Islam.
Hamas vowed to secure Johnston's release after seizing control of Gaza in a violent struggle with rival group Fatah three weeks ago.
Last week the Army of Islam posted a video clip on the internet showing Johnston wearing a belt of explosives.
In the film, Johnston asked the UK government and Hamas not to try to free him by force, saying that negotiations had reached a "very promising" stage.
