Hamas militia members streamed into the streets of a Gaza neighbourhood on Tuesday, closing in on the stronghold where a Palestinian clan is holding kidnapped BBC correspondent Alan Johnston.

Gunmen from the 6,000-strong force secured positions on rooftops and patrolled the roads outside the compound where the shadowy Doghmush clan, the family that controls the little-known group Army of Islam, has been keeping Johnston for nearly four months.

During afternoon clashes, one Palestinian civilian caught in the crossfire was killed, Hamas said. The militant group blamed armed Doghmush forces for the only casualty reported on Tuesday.

"The clocks have begun ticking toward the release of Alan Johnston," Hamas spokesman Ghazi Hamad said.

Security forces "will not spare any efforts to free the British journalist," a spokesman for the Interior Ministry said on Hamas radio. The broadcast also gave a toll-free phone number and urged the public to provide any information about the case.

On Monday, Hamas announced it had captured the Army of Islam's spokesman — a development analysts said could be used as a bargaining chip to negotiate Johnston's release. So far, witnesses said Hamas gunmen have arrested at least four Doghumush members.

New York Times reporter Taghreed El-Khodary told CBC News from Gaza that the Army of Islam had captured 10 Hamas gunmen early Tuesday morning. She said her sources told her one of the captives was the son of a senior Hamas leader. The reports could not be confirmed immediately.

Hamas ultimatum

Although Hamas claims to know where Johnston is being held, the militia has not stormed the facility out of fear that harm may come to Johnston if the hideout is raided. The Army of Islam has already threatened to execute the reporter if Hamas attempts to free him by force, posting an online video clip on June 25 that showed Johnston strapped in an explosives belt.

Last month, a top Hamas official issued an ultimatum warning the Army of Islam that unless it agreed to free Johnston, Hamas would wage an armed invasion to wrest the reporter back safely.

Hamas's hawkish demands for the safe return of Johnston were interpreted in the West as an apparent attempt to win the favour of the international community. The faction staged a violent takeover of the Gaza Strip last month, seizing control of the region from its Western-backed rival, Fatah.

Kidnapped March 12

The Army of Islam, which apparently draws inspiration from al-Qaeda, is believed to have kidnapped Johnston from the Gaza Strip on March 12. He has been held in captivity since then — longer than any Western journalist abducted in Gaza.

Independent Muslim clerics have made efforts to mediate peaceful negotiations, but the Army of Islam said Hamas did not respond.

Meanwhile, Hamas spokesman Fawzi Barhoum accused Johnston's captors of smearing the Palestinian people's reputation and seeking "to prove to the world that we are a group of militias that fight each other to gain personal ends."

In previous tapes, the Army of Islam has demanded that the U.K. government release dozens of captives, including Abu Qatada, a Palestinian-born Islamic cleric suspected of close ties to al-Qaeda.

With files from the Associated Press