Israeli jets have bombed a building in the Gaza Strip which the military says hid a tunnel that Palestinian militants could use to infiltrate Israel.
No-one was hurt in the air strike, to the east of Gaza City.
Israel said the attack was retaliation for a rocket fired from Gaza into its territory on Saturday. The rocket caused no casualties or damage.
Hamas, which controls the Gaza Strip, described the target of the Israeli air strike as "open ground".
However, witnesses said it was a building with two rooms and a courtyard.
An Israeli security source said the tunnel had been dug by Palestinian factions other than Hamas, Reuters reported.
Earlier, Hamas said unidentified Palestinians had detonated explosives at two of its security compounds in Gaza City. No-one was hurt.
Hamas has recently cracked down on possible internal threats from rival Palestinian factions inside Gaza.