GAZA CITY, GAZA — Egypt’s Prime Minister Hisham Qandil visited Gaza Friday and said the Arab world is united behind Palestinians there, as Israel extended its aerial assault and militant groups kept up their barrage of rockets fired at the Jewish state.

Qandil arrived in Gaza with a high-level delegation and called for international efforts to end the three-day-old conflict, in a news conference shown live on Israeli and Arab television stations.

“This tragedy cannot pass in silence and the world should take responsibility in stopping this aggression,” he said.

Israel said it stopped airstrikes while Qandil was in Gaza, after making an earlier pledge to cease fire if there was a corresponding halt in rocket attacks from the territory.

Hamas, which governs Gaza, said the Israeli attacks continued.

Militants from the strip fired 60 rockets at Israel in the past two hours, an Israeli army spokesman said, speaking anonymously in accordance with military rules.

The escalating conflict threatens a region still unbalanced after a wave of popular uprisings last year, including one in Israel’s neighbor Syria that has turned into a civil war.

Israel said yesterday that it’s ready to step up its operation if rocket fire continues, signaling the possibility of the first ground assault on Gaza since the one launched in December 2008, which left more than 1,100 Palestinians and 12 Israelis dead.

Egypt’s Muslim Brotherhood administration, which helped overthrow Israeli ally Hosni Mubarak last year, has vowed to take a stronger stand in defense of Palestinian rights.

Death Toll

Twenty Palestinians have been killed since the airstrikes began, including one man who died this morning while Qandil and Hamas’ Gaza Prime Minister Ismail Haniyeh were visiting a hospital, said Ashraf al-Qedra, spokesman for the Hamas-run ministry of health.

Israel says its airstrikes have targeted launch sites for medium-range rockets, as well as ammunition storage facilities. Three Israelis died in more than 350 rocket attacks launched from Gaza, the Israeli army says.

Army spokesman Brigadier General Yoav Mordechai said the military plans to call up as many as 30,000 reservists, hours after Prime Minister Benjamin Netanyahu said it was ready for a “substantial expansion” of the operation.

The army said in a post on Twitter that it has begun calling up 16,000 reservists.

President Barack Obama’s deputy national security adviser, Ben Rhodes, said that “the onus is on Hamas to de-escalate.”

The United States is in close contact with Israeli officials and is working with Turkey, Egypt, and European nations to pressure Hamas to end the “unacceptable” rocket attacks, Rhodes said during a conference call.

The United States, European Union, and Israel classify Hamas as a terrorist group. The Israeli army advised in a post on Twitter that “no Hamas operatives, whether low-level or senior leaders, show their faces above ground in the days ahead.”