(Adds Israeli air strikes in Gaza, Netanyahu and Abbas comments, updates number of rockets fired at Israel)
JERUSALEM, March 12 (Reuters) - Israel bombed 29 targets in the Gaza Strip on Wednesday, the Israeli military said, after Palestinian militants in the coastal territory fired 60 rockets into Israel in the heaviest such barrage since 2012.
Prime Minister Benjamin Netanyahu said he had ordered the military "to take any action necessary to restore calm" to Israel's south, and that "if there is no quiet in the south then it will be noisy in Gaza, and that's an understatement."
The rocket fire, which police said resulted in no casualties, was claimed by the Islamic Jihad group and came a day after Israel killed three of its members in a Gaza air strike.
A military spokesman said 60 rockets hit Israel "in a simultaneous coordinated attack," and five landed in built-up areas.
Israel bombed 29 militant targets in response, he said.
Israeli forces fired tank shells in response at what the spokesman described as "two terrorist locations" in Gaza.
Israeli warplanes bombed five militant training camps, Palestinian officials and witnesses said.
There were no immediate reports from the Palestinian enclave of any casualties.
"It's a (rocket) barrage such as we haven't seen for two years," Haim Yellin, a local Israeli municipal official in the south, told Army Radio, referring to an eight-day war between Israel and Palestinian militants in Gaza in November 2012.
Sirens sounded in several communities across southern Israel to alert residents to take shelter and general warnings urged everyone in the area to remain indoors.
The Israeli military said it targeted and killed the three Islamic Jihad militants on Tuesday after they fired mortar bombs at Israeli soldiers.
Islamic Jihad said at the time that its men had been killed confronting Israeli troops who had entered the Gaza Strip.
Commenting on Wednesday's barrage, Islamic Jihad said it had fired 90 rockets towards Israel and named the operation "Breaking the Silence."
Palestinian officials said that after the rocket strikes, Israel had informed them that it was closing the Kerem Shalom crossing, through which goods pass into the Gaza Strip, until further notice.
Israel pulled its soldiers and settlers out of the territory, run by Hamas Islamists, in 2005. But it maintained a naval and air blockade and severely restricted the overland movement of people and goods across the volatile border.
Palestinian President Mahmoud Abbas issued a statement via his spokesman urging an end to what he called "Israeli military escalation in the Gaza Strip."
In Washington, the U.S. State Department condemned the rocket attacks and said Israel had a right to defend itself.
"There is no justification for such attacks," spokeswoman Jen Psaki said in a statement. "We call for these terrorist attacks to cease immediately." (Reporting by Jeffrey Heller and Allyn Fisher-Ilan in Jerusalem, Nidal al-Mughrabi in Gaza and Lesley Wroughton in Washington; Editing by Tom Heneghan, Amanda Kwan and Mohammad Zargham)
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