Palestinians in Gaza have fired two rockets into Israel, its military says, hours after Israeli aircraft killed two militants in Gaza, amid rising tension.
The Israeli army said the militants were trying to plant explosives.
The violence comes a day before the second anniversary of Israel's 2008 conflict with Gaza's Hamas rulers.
Last week, an Israeli official warned another war was "only a question of time", while Hamas has threatened a "strong response" to any aggression.
Sunday's clashes began with an Israeli raid on militants from the Islamic Jihad group east of Khan Younis, in southern Gaza.
"Overnight, an IDF [Israeli army] force identified a number of suspects planting explosives along the security fence in the southern Gaza Strip," said an Israeli military statement.
"A combined force, consisting of IAF [Israeli Air Force] helicopters and an armoured force, fired at the suspects and confirmed direct hits."
Islamic Jihad confirmed that "fierce fighting" had taken place, and two of its members had been killed.
Later, the Israeli military said two mortars had landed in the Eshkol region in Israel's southern Negev desert.
The rockets are not thought have caused any injuries.
Two years ago, a 22-day clash between Israeli forces and Palestinian militants in Gaza killed an estimated 1,300 Palestinians, many of them civilians, and 13 Israelis.
Hamas has controlled Gaza since June 2007, after winning elections in 2006 and then forcing its secular rivals Fatah, the party of Palestinian leader Mahmoud Abbas, out of the territory.
Israel says this month alone dozens of missiles have been fired at it from Gaza.
The UN has said more than 60 Palestinians have been killed by Israeli action in Gaza so far this year.
Over the same period, rockets fired from Gaza into Israel have killed one Thai farm worker.