The Palestinian intelligence service's chief has been seriously injured in a blast at the organisation's main office in Gaza City, officials said.
Rival security forces are causing tensions to mount
General Tareq Abu Rajab's staff said he was the victim of a bomb attack they called an assassination attempt.
At least one person died and several others were injured in the blast, after they stepped into a lift.
Correspondents say the incident is set to stoke rising tensions between the rival Hamas and Fatah factions.
A spokesman for Palestinian President Mahmud Abbas condemned the blast.
"The assassination attempt... is a serious escalation and an attempt to undermine national security," he said.
The injured in Saturday's incident at the sea-front intelligence headquarters were rushed to a hospital in Israel, officials said.
Gen Rajab underwent surgery and was reported to be in a stable condition.
Gen Rajab - seen as loyal to Palestinian leader Mahmoud Abbas - had very fraught relations with Hamas and other militant groups in the past and was the victim of a mystery assassination attempt in 2004, the BBC's Alan Johnston in Gaza reports.
An officer in the intelligence service said the blast was caused by a bomb.
This contradicted an earlier statement from the interior ministry which suggested the explosion had been an accident of some kind.
Officials from the Palestinian health ministry initially reported two deaths, but medics later said one person was killed.
Until more details emerge, the incident can only serve to add to the current considerable tension in the area, our correspondent says.
The Hamas-controlled government recently deployed a major force of its militants on the streets.
This was despite intense opposition to the move from the Palestinian presidency which is controlled by Hamas's rival, the Fatah party.
Several people were wounded in clashes between the two factions earlier this week.