Gaza/Tel Aviv - A truce between Israel and militants in the Gaza Strip which has largely held for more than five months was increasingly unravelling Friday, as Gaza gunmen launched another round of rockets into southern Israel.

Israel responded with an air strike on a group of militants in northern Gaza, who had just fired one of the missiles into Israel, an army spokesman in Tel Aviv said.

Four members of the al-Quds Brigades, the armed wing of the radical Islamic Jihad movement, were injured, two of them moderately.

At least 15 rockets hit southern Israel by early afternoon, including some five Iranian-made, Russian-type Grad rockets, two of which struck inside the southern Israeli coastal city of Ashkelon. Two more struck nearby.

In the first such claim of responsibility since the truce, the radical Islamic Hamas movement issued a statement, saying it fired the Grad rockets.

Two smaller Gaza-made rockets also landed inside the Israeli town of Sderot, located just several kilometres to the north-east of the strip. A woman aged about 80 was lightly injured by shrapnel. At least seven other Israelis were evacuated to hospital for shock, Israel Radio reported.

The Gaza truce has been shaking since Israeli troops crossed just over the border with central Gaza late Tuesday last week to destroy a tunnel, which it said was dug under the border by militants who were plotting to abduct soldiers from Israeli territory.

The troops were confronted by local gunmen, sparking the heaviest clashes since the June 19 truce. Five Hamas militants and one Palestinian civilian were killed in the clashes.

Israeli soldiers shot dead four more Hamas militants Wednesday this week as they approached the border with explosives.

An Israeli military spokesman said that during the past 10 days of escalation militants in Gaza had launched at least 70 rockets and mortar shells at Israel.

The Egyptian-brokered, six-month truce is due to expire on December 19 and militants have threatened not to renew it.

Senior Hamas official Ismail Radwan told Israel Radio Friday his movement has asked Egypt to pressure Israel to reopen its crossing points with Gaza, closed since last week in response to the rocket attacks. All Palestinian factions must reevaluate the truce, he said, adding they had yet to form a common position.

Hamas spokesman Ayman Taha told the radio Hamas was interested in keeping the truce, on condition both sides did and Israel re-opened its border crossings to humanitarian aid and fuel.

While Hamas said the Israeli military raid and Israel's border closure were violations of the truce, an Israeli government official said the tunnel dug by militants which had sparked last week's pin- point military incursion, as well as the ensuing rocket fire, were truce violations.

He added however that the "point of no return" had not yet been reached, but if it did, Israel would "not hesitate" to respond more forcefully.

Israeli Defence Minister Ehud Barak ordered Israel's border crossing points with Gaza closed in response to the rocket attacks. Responding to a request to international Middle East envoy Tony Blair, he briefly allowed them to reopen on Tuesday and Wednesday, allowing in 30 trucks of medical supplies and humanitarian aid as well as limited amounts of industrial diesel for Gaza's main power plant. But the crossings were closed again on Thursday.

Gaza's power plant stopped working twice this week, prompting electricity blackouts in Gaza City for several hours on Wednesday night and Thursday night.

Israel has also blocked the entry of journalists and diplomats into Gaza since last week.

The European Commission issued a statement, saying it was "profoundly concerned" by the complete Israeli closure.

"I call on Israel to re-open the crossings for humanitarian and commercial flows, in particular food and medicines," said external relations commissioner Benita Ferrero-Waldner, adding fuel deliveries to Gaza's power plant should also be resumed immediately.

She called on all parties to exercise restraint and avoid a renewed cycle of violence. (dpa)