Palestinians in the Gaza Strip fired two rockets at a southern Israeli coastal 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 concealed rocket launchers in northern Gaza. There were no casualties.
The pre-dawn salvo against 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 the Jewish state.
There was no claim of responsibility for Monday's launches.
They may have been meant to spoil the U.S.-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.
During the previous prisoner release, in August, Gaza militants fired rockets across the border and Israel responded with air strikes.
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 signaled 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 neighboring 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.
Abbas's administration, which was expelled from Gaza in a 2007 Palestinian civil war, has kept Hamas in check in the West Bank. So has Israel, whose troops seized two Hamas lawmakers and 23 other Palestinians in the West Bank on Monday, according to Abbas's administration. Israeli authorities did not immediately comment on the arrests.
The Israeli military spokeswoman said a mortar bomb was fired across the border from Gaza on Sunday, but caused no damage or casualties.