(Adds further Israeli army comment, Israeli-Palestinian talks)

By Nidal al-Mughrabi

GAZA, July 22 (Reuters) - Israel killed four Palestinian gunmen in the Gaza Strip on Sunday, two in a ground assault and two in an air strike on militants launching rockets at the Jewish state, Palestinian witnesses and medics said.

The violence was the worst in coastal Gaza in 10 days, and came a day before Tony Blair makes his first visit to the region as envoy to the Quartet of Middle East power brokers.

Palestinian witnesses said an Israeli attack helicopter opened fire in northern Gaza, killing two militants. The Islamic Jihad group said both were members and had been firing rockets at Israel.

An Israeli military spokesman said the air attack was launched after two rockets slammed into the southern town of Sderot, one striking a school and lightly injuring an Israeli woman.

Both militants killed had been spotted firing the rockets that struck in Sderot, the Israeli spokesman said.

Israel launched a second air strike after dark in Gaza, shooting a missile at a vehicle carrying Hamas militants on a coastal road. The militants escaped unscathed, witnesses and Hamas sources said. The Israeli spokesman confirmed the attack.

Israeli soldiers shot and killed two gunmen of the Hamas Islamist group earlier on Sunday as they approached a border fence with Israel, medics and the Israeli spokesman said.

Hamas, which seized control of Gaza last month, said it sent the gunmen to plant bombs near the fence, targeting Israeli forces.

ARMED INCURSIONS

Israeli troops often shoot at Palestinians who approach the Gaza border with Israel to try to prevent armed infiltrations. Israel also conducts raids in the area to try to stop militants from launching rockets into Israel.

Hamas's violent takeover of Gaza has stirred fears in Israel of a big increase in attacks from the Palestinian enclave.

An Israeli soldier was killed during a raid against militants on July 12, a week after Israel killed 11 Palestinians, including nine militants, in an earlier incursion.

Israeli forces have made preparations to invade the narrow strip to stop a build-up by Hamas and may only have a limited opportunity to launch such an attack, a top army commander said last week.

But Israeli Prime Minister Ehud Olmert seemed to rule out such an operation for now, while the U.S. and Quartet were working to resume peace talks in the region.

"I do not think the way to handle (Gaza militants) should be to go in with a large military force," he said at the weekend.

In advance of Blair's visit, Israeli Foreign Minister Tzipi Livni met in Jerusalem Palestinian Prime Minister Salam Fayyad, holding their second talks since Palestinian President Mahmoud Abbas nominated Fayyad after sacking a cabinet with Hamas.

In their last talks on July 8, Livni and Fayyad discussed ways Israel could ease Israeli restrictions on Palestinian movement in the occupied West Bank.

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