Hamas-run police in Gaza said gunmen killed a Palestinian activist known for supporting Shiite Islamism.
They said Mithqal al-Salmi, 35, was killed Wednesday near his home, and that they are investigating.
The Sunni Islamic terror group Hamas, which rules Gaza, has tense relations with Shiite Iran and the Lebanese Shiite group Hezbollah stemming from the conflict in Syria.
Hamas broke with Iran, a longtime patron, when the group sided with the rebellion against Syrian President Bashar Assad in 2012. Iran and Hezbollah are key allies of Assad.
In February, Hamas arrested al-Salmi after a series of Facebook posts glorifying Iran and Hezbollah, and casting doubt on some Sunni scholars.
Hamas has ruled Gaza since 2007, but more extreme Sunni militant groups also have a presence there.