From Reuters:

Explosions destroyed six cars belonging to members of the Hamas and Islamic Jihad militant groups in Gaza City on Sunday, witnesses said, injuring no one but drawing threats of a response.

… The targeted groups issued a joint statement condemning the attackers as “traitors” – suggesting they thought the perpetrators were fellow Palestinians – and promising that they would be “found and punished”.

No one claimed responsibility, but Hamas, which dominates the coastal enclave, has in recent months faced violent challenges from Palestinians sympathetic to Islamic State or al Qaeda, and who seek stringent religious rule in Gaza and open war with Israel.

Equally problematic ….

Salafists claiming allegiance to Islamic State have begun launching rockets at Israel in defiance of Hamas’ truce with the Jewish state since a war a year ago in which 2,100 Palestinians and 73 Israelis were killed.

Even worse, the Islamic State may seek to seize Gaza.

Last month Islamic State militants fighting Egyptian forces in neighboring Sinai released a video threatening to turn Gaza into another “fiefdom” as in parts of Iraq and Syria.