Palestinian militants on Tuesday fired three homemade rockets into southern Israel, the first such attack since a cease-fire between Israel and Gaza militants took effect last week.
Israel condemned the attack as a "gross violation" of the truce, but did not say whether it would retaliate.
The barrage wounded two people and capped a day of violence that presented the truce with its first serious test.
Just before midnight, Palestinian militants fired a mortar shell into an empty area in southern Israel. And in a pre-dawn raid, Israeli troops killed two Palestinians in the West Bank city of Nablus.
Islamic Jihad, a small armed group backed by Syria and Iran, claimed responsibility for the rocket fire. Although the West Bank is not included in the truce, the group said the Nablus raid had soured the atmosphere of calm.
"We cannot keep our hands tied when this is happening to our brothers in the West Bank," the militant group said.
Hamas spokesman Sami Abu Zuhri said the rocket attack came because of "Israeli provocation this morning" and added that Hamas was "committed to the calm." He said Hamas will talk with other factions and make sure they are committed, too.
The Egyptian-brokered truce went into effect Thursday. The immediate aim was to end fighting that has killed seven Israelis and more than 400 Palestinians - many of them civilians - since Hamas gained control of Gaza a year ago.
It also obliges Israel to ease a punishing blockade of the coastal strip.
In a final stage, the sides are to address Hamas' demand to reopen a major border passage between Gaza and Egypt and Israel's insistence that Hamas release an Israeli soldier it has held for two years.
The cease-fire is meant to avert an Israeli invasion of Gaza, a tiny, impoverished seaside territory of 1.4 million people that Israel evacuated in 2005 after a 38-year military occupation.
The deal extends beyond Hamas to all militant groups operating in Gaza but does not include the West Bank.
Egypt acted as middleman for the six-month truce because Israel, like much of the international community, shuns Hamas for refusing to recognize Israel or renounce violence.
Israeli Prime Minister Ehud Olmert flew to Egypt on Tuesday for talks with Egyptian President Hosni Mubarak.
Upon entering the meeting in the Red Sea resort of Sharm el-Sheik, Mubarak said the two would discuss efforts to release the Israeli soldier, Sgt. Gilad Schalit. Olmert hailed Egyptian efforts to end attacks on Israel from Gaza.
Israel has pressed Egypt to crack down on arms smuggling from Egypt's Sinai desert into Gaza.
On Tuesday, Olmert was quoted in the London-based Al-Sharq Al-Awsat daily as saying that if the smuggling did not end, then Israel would consider the cease-fire agreement violated, and "we will be compelled to military action."
Early Tuesday, Israeli troops killed a senior Islamic Jihad commander in a raid in the West Bank town of Nablus.
A neighbor said a Palestinian bystander was also shot to death by troops when he opened the door of his apartment during the raid. The Israeli military said the man was a militant killed during a gunbattle with troops.
Islamic Jihad said the commander of its northern West Bank operations, Tarek Juma, was killed in the operation.
The military said Juma was targeted because he was planning an attack on Israel. Troops found explosive devices and munitions in his apartment, it said.
In Germany, Palestinian Prime Minister Salam Fayyad condemned the operation.
Fayyad, whose government is trying to negotiate a peace deal with Israel, has said continuing military operations are undermining efforts to have Palestinian security forces restore law and order in the West Bank.
This was "an example of the kind of activity that has to stop and has to stop immediately and promptly if we are going to succeed in providing security to our people," said Fayyad, who is attending an international conference aimed at bolstering his security forces. "There was absolutely no exchange of information on this particular incident."
Also Tuesday, the Hamas military wing took responsibility for a shooting in the West Bank last week that injured three Israeli hikers. The claim was sent in a text message to Gaza journalists.
AP reporter Ali Daraghmeh contributed to this report from Nablus, West Bank.
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