As the Palestinian death toll pushes past 420, much of popular anger throughout the Arab world has been directed at Egypt - seen by many as complicit in the Israeli campaign.

"Israel would not have hit Gaza like this without a green light from Egypt," Hamdi Hassan, MP for the Muslim Brotherhood, Egypt's largest opposition movement, told IPS. "The Egyptian government allowed this assault on Gaza in hopes of finishing off Hamas."

On December 27, Israel began a series of devastating air strikes on targets throughout the Gaza Strip, controlled since the summer of 2007 by Palestinian resistance faction Hamas. According to Israeli officials, the campaign - which has included hundreds of air strikes - comes in retaliation for rockets fired by Palestinian resistance factions.

But on November 4, Israel invaded Gaza and killed seven Hamas members despite a five-month-old cease-fire that had brought calm to the territory. The offensive prompted Palestinian fighters to retaliate by launching rockets into Israel.

Over 200 Palestinians were reportedly killed on the first day of the operation, making it one of the most lethal days for Palestinians in the history of the 60-year-old conflict. Four Israelis - including two Palestinian-Israelis, one of whom was an Israeli soldier - have reportedly been killed by Palestinian rocket fire since the air campaign began.

In the meantime, Israel has continued to amass tanks along its border with the Gaza Strip amid predictions of an imminent ground assault.

"What's happening in Gaza represents an unprecedented crime against humanity," said Hassan. "Enormous military power featuring the latest US weaponry is being brought to bear against a poverty-stricken and largely defenseless population."

Ever since Hamas wrested control of the strip from the US-backed Palestinian Authority (PA) in 2007, Egypt - like Israel - has kept its border with the enclave tightly sealed. The border closures, in tandem with the neutralization of the strip's airports and maritime ports by Israel, has effectively cut the territory off from the rest of the world, and brought it to the brink of humanitarian disaster.

"The international community has condoned the siege of Gaza and allowed the Palestinians to be punished for democratically electing Hamas," said Hassan, noting that the Islamist group swept the 2006 Palestinian legislative elections.

Egypt has said it cannot reopen the Rafah crossing, the sole transit point along Egypt's 14-kilometer border with the Gaza Strip, in the absence of PA officials and EU observers, as stipulated in a 2005 US-sponsored trilateral agreement between Israel, the PA and the EU.

Critics, however, reject this argument, and say there is no legal justification for keeping the border permanently closed to people and goods.

"Egypt isn't even a signatory to the agreement, which expired after one year and was never renewed," said Hassan. "Those cooperating with Israel are simply using this outdated agreement as an excuse to keep Rafah sealed."

Despite increasingly vocal demands - by both street protesters and opposition MPs - to open the border to aid convoys in the wake of the recent Israeli assaults, the Egyptian government has dragged its feet.

"For the first two days of the campaign, the authorities forbade all aid convoys from entering Gaza," Magdi Hussein, secretary general of Egypt's Islamist-leaning Labor Party - officially frozen since 2000 - told IPS. "On the third and fourth days, limited aid was allowed in - but this was only due to mounting popular pressure."

In a televised address on December 30, President Hosni Mubarak defended Egypt's position by again referring to the 2005 border agreement.

"Egypt doesn't want to sanctify the division [between Hamas and the West Bank] by opening the Rafah crossing in the absence of the PA and European observers," Mubarak said.

For the last five days, Egypt has witnessed thousands-strong demonstrations at university campuses, mosques and professional syndicates. Amid an increasingly tight security presence, protesters have called for the permanent reopening of the Rafah border crossing and the severing of Egypt's diplomatic relations with Israel.

"That protests are being staged all over Egypt - and will persist as long as the aggression continues - is an indication of the level of popular outrage," said Hassan. "If the government doesn't change its position and allow aid to flow freely into Gaza, the situation could become very dangerous."

Demonstrators in several Arab capitals have vented their rage outside Egyptian embassies. Protesters have attacked Egyptian consular offices in Sudan and Yemen.

"Protests around Egyptian embassies abroad show that the Arab and Muslim people across the region recognize Egypt's complicity with Israel in keeping the border closed without legal justification," said Hassan.

Suspicions of Egyptian complicity with Israel against Hamas are not limited to the border issue. Many also suspect a degree of Egyptian-Israeli coordination in advance of the air campaign - an impression reinforced by the fact that Israeli Foreign Minister Tzipi Livni was in Cairo, where she met with Mubarak and Foreign Minister Ahmad Abu al-Gheit, less than 48 hours before the assaults began.

At a joint press conference with Abu al-Gheit in Cairo on December 25, Livni vowed to react to retaliatory Palestinian rocket fire from the Gaza Strip. "This is something that has to be stopped," she said. "And this is what we're going to do."

While Abu al-Gheit used the occasion to publicly urge restraint by both sides, independent commentators believe that, while in Cairo, Livni received a tacit go-ahead from Egyptian officials for the campaign.

"It was at the Livni-Mubarak talks that Egypt gave Israel the green light to strike Gaza," said Hassan.

He referred to statements by Hamas spokesman Fawzi Barhoum saying that Hamas had received false assurances from Egypt, immediately after the Cairo talks, that an Israeli attack on the strip was not imminent.

On December 28, a presidential spokesman denied Barhoum's claims. "No Egyptian official sent any assurances to Hamas in this regard," he was quoted as saying in the state press.

Misgivings about possible Egyptian collusion with Israel against Hamas have not been limited to opposition figures and political commentators. On the campaign's third day, thousands of demonstrators in Cairo chanted: "Oh, Mubarak, what do you say? Why was Livni here anyway?"