Israeli forces on a raid in the occupied West Bank exchanged fire on Monday with Palestinian gunmen, Israeli police said, while a Palestinian local official said at least four Palestinians were killed.

The incident occurred in the city of Jenin, where, Israeli police said in a statement, special forces disguised as Palestinians came under heavy fire from “a large number” of attackers while on a mission to detain a militant.

“The undercover forces returned fire towards the terrorists and neutralised them,” the police said.

On Voice of Palestine radio, Jenin’s governor said at least four Palestinians were killed. Israeli police said there were no Israeli casualties.

Later on Monday militants in the Gaza Strip fired a rocket at Israel that was intercepted by the Iron Dome anti-missile system, the military said, in the first such attack since an 11-day war in May.

There was no immediate claim of responsibility for the launching, which Israel’s Kan Radio said could be a response by militants in the Hamas Islamist-run enclave to the killing earlier in the day of the four Palestinians.

Gaza militants have sent incendiary balloons into Israel since a U.N.-brokered ceasefire ended the fighting in May, drawing Israeli air strikes, but held back any rocket fire.

Monday’s rocket launch triggered sirens in southern Israeli communities near the Gaza frontier. Israel has pledged to retaliate as a matter of policy for any attack from Gaza.