Israeli troops have killed a Palestinian militant during a clash in the West Bank town of Tulkarm.
Hamas are taking part in legislative elections for the first time
An Israeli spokeswoman said the soldiers had first tried to arrest him, and he was killed only after he had fired at the troops.
The militant, 24-year-old Thabet Ayyadeh, was the leader of the Hamas military wing in Tulkarm.
A local Hamas political leader accused Israel of seeking to provoke bloodshed and said Hamas would not remain silent.
A self-imposed truce by some Palestinian militant groups expired this month, but correspondents say attacks have been kept largely in check ahead of Palestinian legislative elections on 25 January.
Hamas is expected to emerge from the election as a major power in the Palestinian parliament. The group's political leader in Tulkarm said there would be retaliation.
"This crime was committed while Hamas is abiding by the state of calm.
"The aim is to torpedo the calm. We won't remain silent," Rafat Nasif told the Reuters news agency.