(Adds U.S. comment)
JERUSALEM, March 12 (Reuters) - Palestinian militants in the Gaza Strip fired more than 30 rockets into Israel on Wednesday, the Israeli military said, in the heaviest such barrage in two years.
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 more than 30 rockets hit Israel "in a simultaneous coordinated attack" and that eight landed in built-up areas.
Israeli forces fired tank shells in response at what the spokesman described as "two terrorist locations" in the Gaza Strip. 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.
"It appears as though the waves of rockets have come in response to our preventive operations of yesterday," Israeli Prime Minister Benjamin Netanyahu said in a statement.
"We shall continue to thwart and attack those who seek to attack us, and shall act against them with great force."
Describing the incident on Tuesday in which three Islamic Jihad militants were killed, the military said they were targeted after they fired mortar bombs at Israeli soldiers.
Islamic Jihad said at the time that its men had died confronting Israeli troops who had entered the Gaza Strip.
Commenting on Wednesday's barrage, Islamic Jihad said it had fired 90 rockets toward 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.
In Washington, the U.S. State Department condemned the 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 and Amanda Kwan)