20 rockets fired into Israel
It said the "Iron Dome" defence system had intercepted at least three of the rockets, while the others fell in open areas. No injuries were reported.
The barrage set off air-raid sirens in border communities of southern Israel.
In Gaza, the Islamic Jihad militant group claimed responsibility. It says it fired 20 rockets to avenge the deaths of three members killed in an Israeli air strike.
An Associated Press reporter standing on a balcony saw more than a dozen rockets being fired from the southern outskirts of Gaza City.