The latest in a series of Israeli airstrikes left at least 20 Palestinians dead Thursday, as Israel considers a new invasion of Gaza to confront Hamas.

Reuters reports that Israeli air strikes in Gaza Thursday killed at least 11 militants believed to be involved in rocket attacks against Israeli towns and cities, as well as several civilians, including several children.

The Red Cross and European Union called for restraint as the two-day death toll rose to 33. These included one Israeli, whose death on Wednesday was the first such killing since May, four Palestinian boys who medics said were playing soccer on Thursday, and a baby killed in the bombing of a Hamas ministry.

Dozens more people were wounded in the crowded territory and explosions and gunfire continued well after nightfall.

The bloodiest exchanges in months came days before U.S. Secretary of State Condoleezza Rice returns to the region hoping to invigorate limping peace negotiations between Israel and the anti-Hamas Palestinian leadership in the occupied West Bank.

Israel's deadly attacks on Gaza came the same day that Palestinian militants launched a barrage of long-range rockets at the city of Ashkelon, reports The New York Times. Noting that the rocket attack was the largest Ashkelon has ever suffered, The Times writes that the Israeli government considers it a sign of an escalation in hostilities by Hamas, which controls Gaza.

No one was hurt in the attacks on Ashkelon, a city of 120,000 whose center lies about 10 miles north of the Gaza Strip, but there was significant damage to the building that was hit, said Micky Rosenfeld, an Israeli police spokesman. Six of the rockets hit central areas and residential neighborhoods, he said, while the others landed in open fields outside the city. ...

David Baker, an Israeli government spokesman, said the attacks constituted "a definite escalation, and one that we will not tolerate." He said Israel was "well aware of the steps it must take to halt the rocket fire," but did not elaborate on any additional Israeli response.

The Times notes that this week's violence was touched off early Wednesday, when an Israeli airstrike killed five Palestinian militants in southern Gaza. Hamas responded with a rocket attack on the town of Sderot, killing one man, the first Israeli victim of rocket fire in nine months.

The BBC reports that Deputy Defense Minister Matan Vilnai went so far as to warn Palestinians that continued rocket attacks would bring about a "bigger holocaust."

"The more [rocket] fire intensifies and the rockets reach a longer range, they (the Palestinians) will bring upon themselves a bigger holocaust because we will use all our might to defend ourselves," Matan Vilnai told Israeli army radio.

Correspondents say the "holocaust" is a term rarely used in Israel outside discussions of the Nazi genocide during World War II.

Haaretz notes that a spokesman for Mr. Vilnai says that he used the word "holocaust" in the sense of disaster, and "did not mean to make any allusion to genocide."

The latest round of violence appears to have Israel preparing for a new offensive against Hamas. Haaretz reports that several members of the Israeli Knesset have called for an invasion of Gaza to prevent further rocket attacks.

"The State of Israel must make a strategic decision to order the IDF to prepare quickly to topple the Hamas terror regime and take over all the areas from which rockets are fired on Israel," MK Tzachi Hanegbi (Kadima) told Israel Radio. He said the IDF should prepare to remain in those areas for years.

MK Gideon Sa'ar (Likud) said his party would back an invasion of Gaza, though he fell short of advocating reoccupation.

"There is no doubt that the security response needs to include a ground component," said Sa'ar. He said the "takeover of territory in the northern Strip" from which the Palestinians launch rockets at Israel would reduce the barrages from Gaza.

Such an invasion may be in the works. The Associated Press reports that while "Israel does not intend to launch a major ground offensive in the next week or two... the army has now completed its preparations and informed the government it's ready to move immediately when the order is given," according to an Israeli official speaking on condition of anonymity. And The New York Sun writes that Israel has begun to inform foreign intermediaries between Israel and the Palestinians that a major offensive may be on the way.

Defense Minister Ehud Barak said during a closed-door meeting with aides yesterday in Jerusalem that Israel has begun preparing "the international community" — foreign officials involved in negotiations with the Palestinian Arabs, including a former British prime minister, Tony Blair — for a "large ground operation" in Gaza, several Israeli press outlets reported.

"If there is one more fatality, Israel may have to go in," a Western diplomat who asked not to be named said. Since the killing Wednesday of Roni Yihye by a rocket from Gaza — the first such Israeli fatality in several months — a growing number of Israeli officials, opinion makers, and politicians have searched for ways to counter the increasing accuracy and range of the Palestinian Arab rockets.

"This is not an easy decision, but it may be necessary. We have to break the Hamas military power," a former Israeli deputy defense minister, Ephraim Sneh, told The New York Sun.