U.S. envoy George Mitchell said on Thursday opening the Gaza Strip to commercial goods would help to choke off the smuggling that Israel fears could replenish Hamas's weapons stocks.

But he said the Palestinian Authority of President Mahmoud Abbas must help to supervise the crossings, a demand that has been a major sticking point in Egyptian-brokered negotiations with the Gaza Strip's Hamas rulers for a long-term ceasefire.

"To be successful in preventing the illicit traffic of arms into Gaza, there must be a mechanism to allow the flow of legal goods, and that should be with the participation of the Palestinian Authority," Mitchell said after meeting Abbas.

Abbas's Western-backed Palestinian Authority holds sway only in the West Bank after Hamas wrested control of the Gaza Strip from his Fatah movement in fighting in 2007.

Rocket attacks from Gaza and Israeli air strikes over the past two days have threatened to undermine Mitchell's efforts to consolidate a fragile truce between Israel and Hamas that went into effect on January 18, ending 22 days of fighting.

Militants launched one rocket from Gaza into Israel late on Wednesday, the first since the January 18 ceasefire, and another on Thursday. No one was hurt.

Israeli aircraft then struck in the southern Gaza Strip, attacking a metal workshop that the military called a weapons factory, causing no casualties; and a motorcycle, wounding two militants and 10 youths passing by, medical workers said.

While Israel said ending rocket fire at its towns was the main aim of its assault on Gaza, Hamas insists there can be no lasting truce until Israel ends a near-total blockade of goods traffic into Gaza, tightened when Hamas came to power.

U.S. President Barack Obama dispatched Mitchell on his week-long mission in an early signal of the new administration's commitment to promote Israeli-Palestinian peace talks.

Speaking on Al Aqsa TV, Ismail Haniyeh, Hamas's leader in the Gaza Strip, cited Obama's campaign pledge to bring change after the Bush presidency.

"We are hopeful that there will be a full review by the president and his administration regarding the Middle East and specifically the Palestinian case," Haniyeh said.

But with the February 10 election approaching, Israeli leaders have been talking tough on security, a main voter concern.

They have pledged a strong response to a blast that killed an Israeli soldier on the Gaza border on Tuesday and to the rockets. Palestinian militants said the rockets were payback for Israel's killing of three Palestinians since the truce began.

Some 1,300 Palestinians, including at least 700 civilians, were killed during Israel's Gaza offensive, according to the Hamas-run Health Ministry in the territory. Israel put its losses at 10 soldiers and three civilians.

Foreign Minister Tzipi Livni, a candidate for prime minister, said the government will not restrain itself even if militants fire only a few rockets.

"Our strategic objective is to restore calm to the south, but if they (Hamas) do not understand this through one operation, there will be more. And if they do not understand this through military operations, we will complete our objective by bringing about their downfall," Livni said.

Opposition leader Benjamin Netanyahu, who tops opinion polls ahead of the election, saw more violence ahead.

"It's clear Hamas is rearming. Of course it's attacking us. Of course it's trying us," Netanyahu told Israel Radio. "The next government will have no choice but to finish the work and remove the Iranian terror base for good."

Israel has secured U.S. and European pledges to help to prevent Hamas, which it says receives weapons from Iran, from rearming through tunnels under the Gaza-Egypt border and by sea.

Egypt has also limited movement through its Rafah crossing with the Gaza Strip.

But the tunnels have been the only way for Gazans to get the commercial goods that Israel keeps out, and they have begun to rebuild the ones that Israeli bombs destroyed.

Haniyeh said a ceasefire deal "must guarantee the lifting of the siege."

Under a 2005 agreement brokered by the United States, the Palestinian Authority was to help to oversee border crossings. The deal gives Hamas no role.

Israeli Prime Minister Ehud Olmert told Mitchell on Wednesday that Israel would not reopen any Gaza crossings, except for aid shipments, until an Israeli soldier captured in 2006 was freed, an Israeli official said.

The United Nations on Thursday launched an appeal for $613 million for emergency humanitarian aid and rebuilding in Gaza.