Hamas gunmen on Tuesday took up positions around the stronghold of the shadowy group holding kidnapped British journalist Alan Johnston, stepping up the pressure to secure the correspondent's release. Members of Hamas' 6,000-strong militia moved onto rooftops of high-rise buildings and deployed gunmen in streets in the Gaza City neighborhood inhabited by the Doghmush clan. The large, heavily armed family leads the Army of Islam, a little known group that has been holding Johnston for nearly four months. Interior Ministry spokesman Khaled Abu Hilal said security forces "will not spare any efforts to free the British journalist." Hamas radio also broadcast a toll free phone number, urging people to call in any information about the case. Witnesses said at least four members of the Doghmush clan were detained by Hamas. Since seizing control of Gaza last month, Hamas has demanded Johnston's release in an apparent bid to gain favor with the West.