Israel has struck dozens of targets in the Gaza Strip, the Israeli military says, and Palestinian militants have fired their heaviest rocket salvoes across the border since August.
There were no casualties reported in either Israel or Gaza, which is controlled by the Islamist Hamas group.
The Palestinian Islamic Jihad, one of the other armed groups that operates in Gaza, said in a statement it had fired the rockets in response to Israel's killing of four Palestinian protesters on Friday near the border.
"The Islamic Jihad will abide by a ceasefire as long as the enemy abides by it. Should bombardment and aggression continue, the resistance will respond," the group said.
Israeli military spokesman Lieutenant-Colonel Jonathan Conricus accused Syria and Iran of involvement in the attack.
"Orders and incentives were given from Damascus with a clear involvement of the Iranian Revolutionary Guards al-Quds force," Conricus told reporters. "Our response is not limited geographically."
Israel regularly accuses Iran of aiding Gaza militants, but rarely levels the charge in connection with a specific rocket attack.
Islamic Jihad had no immediate comment.
The Israeli military also said it holds Hamas accountable for the events in Gaza. It said its air force hit more than 80 targets including a four-storey building used by Hamas as a headquarters, in response to more than 30 rockets launched into Israel. There was no immediate comment from Hamas.
In Israel, warning sirens sounded through the night in communities near the Gaza border, sending residents of to bomb shelters. Some rockets were intercepted.
In Gaza, where militants usually vacate potential targets when violence flares, explosions lit up the night sky.
The flare-up began after the four Palestinians were killed by Israeli troops on Friday during weekly protests along the border. Israel said its forces were attacked with explosive devices and that some demonstrators breached the border.
Palestinians have been protesting along the frontier since March 30, demanding an end to Israel's blockade of the territory and the right to return to lands from which they fled or were driven from when Israel was founded in 1948.
According to the Palestinian Health Ministry, 213 Gazans have been killed by Israeli forces during the protests. An Israeli soldier was killed by a Palestinian sniper.
Egyptian security officials have been talking separately to Israeli and Palestinian leaders in an attempt to restore calm along the border.
