Israeli warplanes struck at least four times across Gaza on Friday, damaging a number of structures that the Israeli military said were sites for weapons manufacturing or storage.

A workshop destroyed early Friday morning in Israeli airstrikes in Gaza City.

A military spokesman said the strikes were in response to a Qassam rocket fired from Gaza on Thursday that hit the Ashkelon area on Israel’s central coast. The spokesman added that nearly 20 rockets or mortars had come from Gaza during March, and more than 40 since the beginning of the year.

Most of the targets in Friday’s airstrikes belonged to Hamas, including two training camps, according to Palestinians in Gaza. One of the camps was located near a cheese factory in the southern part of Gaza City, and three Palestinian children, including a 1-year-old, were lightly wounded by flying glass near the factory, according to Mu’awia Hassanein, an official with the Health Ministry.

A police station near the al-Maghazi refugee camp and the entrance to a Hamas media production facility in a former Jewish settlement also were hit.

The Israeli military spokesman said he had no information on the factory or on other strikes.

Al-Aqsa, the Hamas-run television station, reported that Ismail Haniya, the leader of the Hamas government in Gaza, had condemned the Israeli attacks. The channel also said that his government was contacting other Palestinian factions in an attempt to maintain calm.

Tensions have risen along the Gaza border in recent weeks. A week ago, two Israeli soldiers were killed when, according to the army, they were pursuing militants trying to lay explosives near the border fence.

In December 2008, Israel launched a three-week war on Gaza to stop the rocket fire. Since then, the rockets had mostly stopped. Those that were fired have been attributed to groups other than Hamas, which controls Gaza.

But the Israeli military said the border incident last week was claimed by Hamas.

A farm worker from Thailand was killed on March 18 in Israel by a rocket fired from Gaza. The attack came soon after the arrival in Gaza of the European Union’s top foreign policy official, Catherine Ashton.

Ansar al-Sunna, a small jihadist group that challenges Hamas, claimed responsibility for that attack.

The worker, Manee Singueanphon, 30, was the first person to die from Gaza rocket fire since January 2009 and the end of the three-week military offensive. The rocket struck an Israeli cooperative farm called Nativ Haasara, near the Gaza border.

The day after the attack, Israeli aircraft fired several missiles at Gaza targets, including smuggling tunnels under the Gaza-Egypt border and a metal workshop in Gaza City, Hamas security officials said at the time.

Gaza, the Palestinian coastal enclave, has been largely isolated since it came under the control of Hamas, which has refused to accept the conditions established by the international group that focuses on the Middle East, the so-called quartet — the United States, the European Union, the United Nations and Russia. Those conditions include a renunciation of violence, the recognition of Israel’s right to exist and the acceptance of previous agreements between Israel and the Palestine Liberation Organization.