A spokesman said the projectile landed in an open field near the town of Sderot, a frequent target of such attacks in the years leading up to the devastating offensive Israel launched against the Hamas-ruled territory in December 2008.
Israeli forces meanwhile arrested a local Hamas leader, Sheikh Shaker Amara, 50, near the West Bank town of Jericho, a Palestinian security official said.
Israel has been combing the occupied West Bank in search of Hamas militants who allegedly killed four Israeli settlers in a drive-by shooting last week ahead of the relaunch of Middle East peace talks in Washington.
The Hamas movement, which has controlled Gaza since June 2007, is vehemently opposed to the new negotiations and last week vowed to carry out further attacks.
Since the end of Israel's 22-day offensive against Gaza in January 2009, Hamas has reined in rocket fire. But more than 100 rockets or mortar rounds have been fired from the territory since the start of the year, according to the Israeli military.
Hamas has not claimed any of the attacks, which are believed to have been carried out by smaller, more hardline factions.
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