The hard-line stance, voiced by a senior Hamas official at the group's first rally since a cease-fire in the Gaza war took effect on Tuesday, signaled that indirect negotiations in Cairo over a permanent truce in Gaza were not making headway. It was an ominous sign ahead of Friday's expiration of a temporary three-day truce that ended a month of fighting.
A text message from Hamas' military wing, the Izzedine al-Qassam Brigades, warned there would be no extension of the cease-fire if there was no agreement to permanently lift the blockade enforced by Israel and Egypt since the militant group overran Gaza in 2007.
Abu Obeida, the al-Qassam spokesman, appeared on the group's Al-Aqsa TV station and said Hamas was "ready to go to war again." He threatened to launch a long-term war of attrition that would cripple life in Israel's big cities and disrupt air traffic at Israel's international airport in Tel Aviv.
He also appealed to Hamas negotiators in Egypt not to accept an extension of the cease-fire without an agreement on lifting the blockade. "The resistance is capable of imposing its conditions," he said.
A security official in Egypt said Egyptian negotiators were struggling to bring the two sides closer together, with one official saying Hamas and other Gaza militants were refusing to compromise.
Israeli Prime Minister Benjamin Netanyahu vowed a tough reaction if Hamas renews hostilities.
"They might reject an extension. If they attack us, we'll respond in kind, as any government would," he told Germany's ZDF television.
An Israeli defense official said Israel would respond "forcefully," and that Netanyahu and his defense minister, Moshe Yaalon, had instructed the military "to be ready for anything." He spoke on condition of anonymity because he was not authorized to talk to the media.
About 2,000 people showed up for Hamas' rally in the heart of Gaza City on Thursday, well below the levels of similar gatherings on previous occasions.
The modest turnout was not necessarily a sign of waning support for the group, but most likely a reflection of the fatigue felt by most of Gaza's 1.8 million residents after four weeks of a ruinous war, as well as anxiety over whether the three-day truce will be extended.
"Our fingers are on the trigger and our rockets are trained at Tel Aviv," al-Masri told the rally.
In the fighting, nearly 1,900 Palestinians, three-quarters of them civilians, have been killed, more than 9,000 wounded and some 250,000 people made homeless, according to Palestinian medical officials and the United Nations. Israel lost 64 soldiers and three civilians.
Hamas, meanwhile, announced that Ayman Taha, a former spokesman for the group, on Thursday died of wounds he had sustained in an Israeli airstrike on a makeshift Hamas detention center 11 days earlier. Taha had been detained by Hamas security in January, though the charges against him were never made public. Before his arrest, Taha had also served as a liaison with Egypt.
He was the first senior member of the Hamas political leadership to be killed in this war.
Cairo has been mediating indirect talks between Israel and Hamas on extending the 72-hour cease-fire that expires Friday morning.
Hamas has demanded the lifting of an Israeli and Egyptian blockade imposed on the coastal territory. Israel has said the militants must disarm first, which al-Masri rejected.
"It is out of the question that the weapons of the resistance should be on the negotiating table. They have not been put on the table and, God willing, they will never be," he said.
Al-Masri also insisted that Hamas fighters were "in good shape" despite four weeks of fighting and the group still had tunnels extending into Israel that could be used for attacks if the group's demands are not met.
Addressing communities in southern Israel close to Gaza, an area that suffered the most from Hamas rockets, he said: "You are advised not to return to your homes ... Netanyahu is gambling with your lives for political gain."
The blockade, which Israel says is needed to prevent weapons from reaching Gaza, has led to widespread hardship in the Mediterranean seaside territory. Movement in and out of Gaza is limited, and the economy has ground to a standstill and unemployment is over 50 percent. While Hamas is shunned by the West as a terrorist group, there is a widespread consensus in the international community that the blockade must be eased.
"Without the full lifting of the blockade of the Gaza Strip, Palestinians in Gaza will continue to be deprived of any sense of a normal life and the massive reconstruction effort now required will be impossible," James W. Rawley, the U.N. Resident and Humanitarian Coordinator for the occupied Palestinian territory, said in a statement.
Late on Wednesday, U.N. Secretary-General Ban Ki-moon weighed in again on the Hamas-Israel conflict, demanding an end to what he called the senseless cycle of suffering, telling the General Assembly that "the massive deaths and destruction in Gaza have shocked and shamed the world."
He also urged the international community to support the enormous task of rebuilding Gaza, providing humanitarian aid to thousands in need and treating the wounded.
An EU proposal to help end the Gaza conflict has, meanwhile, been gaining traction across Europe.
The proposal calls for reopening an EU monitoring mission along the Gaza-Egypt border.
In addition, the international community should help build a Gaza seaport for goods and passengers, with international inspection points both in Gaza and in a transit harbor in Larnaca, Cyprus, to make sure weapons do not get smuggled in, said an official with access to deliberations of European diplomats in the region. The Cyprus government has said it could be used as "a repository" destined for Gaza.
Rawley offered a glimpse of the scope of reconstruction needed in Gaza. He said 10,000 housing units have been destroyed or badly damaged, and the 65,000 people had no home to go to.
The war grew out of the killing of three Israeli teens in the West Bank in June. Israel blamed the killings on Hamas and launched a massive arrest campaign, rounding up hundreds of its members in the West Bank, as Hamas and other militants unleashed rocket fire from Gaza.
On July 8 Israel launched an air campaign on the coastal territory, sending in ground troops nine days later to target rocket launchers and cross-border tunnels built by Hamas for attacks inside Israel.
Michael reported from Cairo. Associated Press reporters Ibrahim Barzak in Gaza City, Ian Deitch in Jerusalem and Raf Cassert in Brussels, Belgium contributed to this report.