Hamas on Monday arrested the spokesman of a shadowy group holding British reporter Alan Johnston, a move that could give it a bargaining chip to secure the Briton's release.
Hamas has demanded that the Army of Islam, led by a violent Gaza clan, free Johnston, who was kidnapped on a Gaza City street on March 12.
But the group, whose formerly close relations with Hamas have soured, has demanded that Britain first release a radical Islamic cleric with ties to al-Qaida. It has vowed to kill Johnston if Hamas tried to free him by force.
The Army of Islam threatened to release what it said were damaging documents about Hamas if its spokesman, Abu Khatab al-Maqdisi, weren't freed. It also kidnapped 10 members of Hamas, the Islamic group whose violent takeover of the Gaza Strip last month has not empowered it enough to secure Johnston's release.
Al-Maqdisi was arrested while trying to fire on members of a Hamas-allied security force, said Sami Abu Zuhri, a senior Hamas official. The Army of Islam said in a statement that its spokesman was leaving early morning prayers.
Abu Zuhri denied any link between al-Maqdisi's arrest and efforts to free Johnston.
Al-Maqdisi, he said, "was arrested in a gunbattle."
In a statement posted on militant web sites, the Army of Islam threatened to release documents suggesting misconduct among Hamas members. "We will release some documents that reveal the truth about some personalities who have tricked the Muslim community," the statement said.
Johnston's disappearance is the longest of any Western journalist abducted in Gaza. Palestinian officials have said they know where to find Johnston, but have held back on raiding the hideout at Britain's request, for fear of harming him.
Last week, the Army of Islam posted a video message from Johnston on a militant Web site in which he said he was dressed in an explosive belt that his captors would detonate if there was an attempt to storm the Gaza City hideout where he is being held.
The tit-for-tat arrest and kidnappings reflect new tensions between Hamas and the Army of Islam, which was also involved in the capture of Israeli Cpl. Gilad Shalit more than a year ago.