(IsraelNN.com) Gaza terrorists have upgraded their mortars and changed their tactics, catching IDF troops by surprise over the Sabbath in an intense mortar attack on the Nahal Oz army base.

IDF Sgt. Noam Nakash, 21, of Be'er Sheva lost his leg in the Friday night attack and is being treated at Barzilai Hospital in Ashkelon. Three IDF soldiers suffered moderate-to-serious wounds, and four others were lightly injured. All were evacuated to Soroka Medical Center in Be'er Sheva.

The Hamas terrorist organization has acquired advanced 120-mm mortar shells that are more accurate and lethal than the previous models, according to a report by Sunday morning by Voice of Israel government radio military correspondent Carmela Menashe.

The Al Qassam Brigades division of Hamas, which took responsibility for the shelling, said it had carried out the attack "as a response to Zionist aggression… and against the occupation."

The attack came just 24 hours after Israel said it was prepared to continue the temporary truce that began on June 19, which had completely disintegrated over the past four weeks.

Defense Ministry Chief of Security and Political Affairs Amos Gilad told Egyptian intelligence head Omar Suleiman that Israel would agree to re-open the Gaza crossing to commercial traffic on the condition that Hamas cease its attacks.

Israel has periodically opened the crossings for delivery of humanitarian aid to the region, sometimes even while sporadic rocket attacks continued. Moreover, Palestinian Authority Arab residents of Gaza have continued to cross into pre-1967 Israel for medical treatment through the Erez Crossing.

Hamas has adopted a routine of planting bombs along the Gaza separation barrier, and using the provocation to draw counterterrorist fire by IDF soldiers. The terrorists then respond by firing mortar shells with a range that can reach as far as the nearby army bases.

Soldiers have complained that there is no fortification in their bases against Kassam rocket attacks, but government officials have said that it is impractical to protect every soldier by rocket-proofing the housing.

Deputy Defense Minister Matan Vilnai repeated stale threats issued a year ago by outgoing Prime Minister Ehud Olmert and Defense Minister Ehud Barak that Israel "soon will have no choice" other than to stage an all-out offensive against Hamas.

The terror group has had a death grip over Gaza since it wrested total control over the region in a militia war with rival Fatah faction in June 2007. Despite a temporary truce with Jerusalem that began on June 19, there were sporadic violations with single and double Kassam rocket attacks on the western Negev and Gaza Belt region.

Four weeks ago, the temporary truce was destroyed with the discovery that Hamas operatives had prepared a tunnel some 250 meters from the security barrier with which they planned to kidnap another IDF soldier. Aside from the fact that the tunnel itself was a complete violation of the ceasefire, Israel's government decided its existence merited an immediate and unequivocal response, and sent the army to destroy it. Hamas responded with weeks of intensified rocket and mortar attacks on southern Israel.