Israel Defense Forces troops on Saturday attacked two groups of Palestinian militants firing mortar shells in the northern Gaza Strip, wounding four Hamas gunmen, Israeli and Palestinian officials said.

Witnesses said the clashes occurred near the Nahal Oz fuel depot on the border between Israel and Gaza. The depot, which pumps fuel into Gaza, is a frequent target of Palestinian militants, who view the crossing as a symbol of Israel's economic blockade of the area.

Hamas, which has ruled Gaza for nearly a year, said its gunmen were firing machine guns at the troops when they were struck. But local residents said the militants were firing mortar shells. The residents spoke on condition of anonymity, fearing retribution from Hamas.

Later Saturday, two more militants were wounded while firing mortar shells, Hamas said.

Palestinian medical officials said one of the wounded was in critical condition.

The IDF confirmed both attacks, including an airstrike. It said militants fired mortar shells and a homemade rocket at the fuel depot.

The clashes occurred as Egyptian mediators try to wrap up a cease-fire between Israel and militants in Gaza. Amos Gilad, a senior Israeli defense official, is expected to travel to Egypt on Sunday as part of that effort.

Israeli troops and Palestinian militants have frequently clashed since Hamas violently seized control of Gaza last June.

Seeking to step up pressure on Hamas, Israel has sealed its border crossings with Gaza and imposed other economic sanctions, causing shortages of fuel, electricity and many basic goods.

Hamas wants Israel to ease the blockade under the cease-fire - a demand Israel is not expected to meet in the near future.