Palestinians in the Gaza Strip fired two rockets at a southern Israeli port city on Monday and Israel's Iron Dome interceptor shot down one while the other fell into the sea, a military spokeswoman said.
Within hours, Israel's air force bombed what a military spokesman described as "two rocket-launching tubes" in northern Gaza.
There were no casualties. The pre-dawn Palestinian salvo on Ashkelon, about 12 km (7 miles) north of Gaza, was unusual given the relative restraint of Palestinian militants since last November's war between the coastal enclave's Islamist Hamas rulers and Israel.
There was no immediate claim of responsibility for Monday's launches. It may have been meant to spoil the US-sponsored peace talks that Hamas's rival, Palestinian President Mahmoud Abbas, resumed with Israel in July. To bolster Abbas, Israel is due to free 26 Palestinian prisoners this week.
Hamas has called on Abbas, who holds sway in the Israeli-occupied West Bank, to abandon peacemaking and form a new Palestinian power-sharing government. The Islamist faction has also signalled readiness to go to war, taking responsibility last week for a tunnel which the Israelis discovered running into their territory from Gaza and said was likely intended for kidnapping soldiers or setting off underground explosives.
But the sands are shifting for Hamas, which has tipped into financial and political crisis after being cut off from neighbouring Egypt by the new, military-guided interim government in Cairo.
Hamas's ties with former backers Iran and Syria have similarly deteriorated, and in Gaza its authority has at times been challenged by more radical armed Islamists. The Israeli military spokeswoman said a mortar bomb was fired across the border from Gaza on Sunday, but caused no damage or casualties.