Israel's military has fired on Hamas installations in Gaza after a rocket launched from the territory exploded inside Israel.
Hamas, the Islamic militant group that rules Gaza, has largely adhered to a ceasefire which ended a 50-day war with Israel in 2014, but other militant groups occasionally fire rockets or mortar rounds over the frontier.
Israel holds Hamas responsible for all incoming fire.
There were no reports of casualties on either side.
Sirens wailed in parts of southern Israel warning of incoming rockets, with one said to have exploded in an open field.
Soon afterwards, an Israeli tank fired at a Hamas position near the frontier.
Hours later, Gaza residents said Israeli air strikes targeted three Hamas-run militant training sites.
Israeli military spokesman Lt Col Peter Lerner said the military "will not tolerate rocket fire toward civilians and will continue to ensure security and stability in the region".
There was no immediate claim of responsibility in Gaza for the rocket attack. Jihadists who support Islamic State have said they were behind similar attacks in the pas