JERUSALEM — Thirteen Palestinian Arabs, including a cameraman working for Reuters, were killed in Israeli air strikes in the Gaza strip as fighting brought the number of casualties to 21 since early yesterday.

Twelve Palestinian Arabs died when Israeli missiles struck east of the al-Bureij refugee camp in central Gaza, the chief of emergency services at the Palestinian Health Ministry, Mo’aweya Hassanein, told reporters. Shortly afterward, an Israeli missile hit a jeep in the same area carrying a Reuters cameraman, Faddel Shana’a, killing him, Mr. Hassanein said.

Earlier in the day, four Hamas gunmen and three Israeli soldiers were killed in fighting in eastern Gaza, the Israel Defense Forces and the Islamic movement said. A gunman from the Popular Front for Liberation of Palestine was killed in a clash with troops in the southern Gaza town of Rafah, the group said in a statement.

Violence has grown in the week since Gaza militants infiltrated Israel, killing two people near the Nahal Oz crossing. Israel has imposed an economic and military blockade of the Gaza strip to stop rocket attacks launched by militants and to undermine Hamas, which seized power there in June. A spokesman for the Israel Defense Forces, speaking on condition of anonymity, said forces had targeted a group of armed men near al-Bureij but was checking reports that it may have hit civilians. Reuters’s editor in chief, David Schlesinger, called for an investigation into the death of Shana’a, 23, the news agency said. As the two sides clashed in Gaza, militants fired about 10 Qassam rockets and a number of mortar shells at the western Negev in the morning, Israel’s Haaretz daily reported. It said there were no casualties.

Israel continues to block the entry of fuel to Gaza, after Defense minister Ehud Barak ordered the resumption of deliveries of cooking gas and diesel for Gaza’s sole power plant, Mahmoud al-Khozendar, of the Gaza gas stations owners’ union, told reporters in Gaza City. Fuel deliveries hadn’t resumed because the transfer terminal at Nahal Oz was being inspected for possible damage done during last week’s fighting, the army said.

An Islamic Jihad militant was killed and two bystanders wounded late Tuesday when an Israeli drone aircraft fired a missile at him as he drove his motorcycle in the Jabalia refugee camp in northern Gaza, the group said. The Israeli army said it hit unidentified targets in two air raids, without providing further details.