President Barack Obama's new Mideast envoy sought Wednesday to boost a 10-day-old Gaza cease-fire that was thrown into turmoil, as Israeli warplanes pounded Gaza smuggling tunnels in retaliation for a Palestinian bombing that killed a soldier.

As the Israeli Cabinet met to consider how far to go in its response to Tuesday's bombing, U.S. envoy George Mitchell said it was "critical" that the cease-fire be extended and consolidated."

Mitchell's tour launches the first Mideast foray of the new Obama administration. Obama said his envoy would listen to all sides to then craft an approach for moving forward with stalled Israeli-Palestinian peace efforts.

Click to view photos from the conflict.

"The United States is committed to vigorously pursuing lasting peace and stability in the region," Mitchell said after talks with Egyptian President Hosni Mubarak in Cairo, his first stop before heading to Jerusalem later in the day. He said his tour less than a week after Obama's inauguration "is clear and tangible evidence to this commitment."

But the new violence cast a shadow over Mitchell's arrival.

The flare-up is the worst since Israel and Hamas separately declared cease-fires on Jan. 18 to end a three-week Israeli offensive against the Palestinian militant group in the Gaza Strip. Since withdrawing its troops, Israel has threatened to retaliate hard for any violations of the informal truce.

Reflecting the seriousness of the situation, Defense Minister Ehud Barak canceled a planned trip to Washington this week to stay home and deal with the crisis, defense officials said.

The soldier was killed Tuesday on Israel's frontier with the Gaza Strip by a roadside bomb planted on the Gaza side and set off by remote control, the military said. Three other soldiers patrolling the border were injured.

Israel responded swiftly, sending tanks and bulldozers into northern Gaza to plow up the attack site and launching an airstrike that wounded a Hamas militant "who was prominent in the organization accountable for the attack," the military said. Hamas said the Israeli strike injured one of its men as he rode a motorcycle in the southern Gaza town of Khan Younis.

Airstrikes early Wednesday targeted the network of tunnels used to smuggle arms, money and people into Gaza from Egypt. Israel bombed the tunnels heavily during the war, but smugglers resumed work after the cease-fire.

There was no claim of responsibility for Tuesday's bombing, but Ramattan, a Palestinian news agency, released a video of the roadside bombing allegedly filmed by militants it did not identify.

"Hamas unfortunately controls the Gaza strip and is directly responsible for all hostile fire from Gaza into Israel," government spokesman Mark Regev told The Associated Press.

"Israel wants the quiet in the south to continue but yesterday's attack is a deliberate provocation designed to undermine and torpedo the calm. If Hamas acts to undermine the cease-fire, it will have no one but itself to blame for the consequences," he said.

Ahead of Mitchell's arrival, Obama said his envoy would listen to all sides to then craft an approach for moving forward with stalled Israeli-Palestinian peace efforts.

Before his tour, Israeli officials said Mitchell would also discuss ways to solidify the cease-fire into a longer term truce — a complicated prospect that will require international arrangements to ensure that border crossings into Gaza are opened while preventing Hamas from rearming by smuggling in weapons.

The Israeli offensive killed nearly 1,300 people, including hundreds of civilians, and caused an estimated $2 billion in damage. The international community is trying to broker a long-term cease-fire and figure out how to rebuild the coastal territory.

In Cairo, Mitchell met with Egyptian President Hosni Mubarak. The American envoy was to head later in the day to Jerusalem for a three-day visit that is to include meetings with Prime Minister Ehud Olmert, top security officials and pro-Western Palestinian President Mahmoud Abbas in the West Bank.

Mitchell has no plans to meet with Hamas, which the U.S., Israel and European Union consider a terrorist group. Hamas seized Gaza from forces loyal to Abbas in June 2007. Hamas' control of Gaza, and its refusal to recognize Israel's right to exist, are considered major obstacles to peace efforts.

Jewish settlers in the West Bank were planning a Jerusalem demonstration to coincide with the visit by Mitchell, who in a 2001 report urged Israel to freeze settlements in the West Bank.

Yishay Hollender, a spokesman for settlers' umbrella group, the Yesha Council, said settlers will drive to Jerusalem a float depicting the dangers to Israel of a Palestinian state as a "reception" for Mitchell.

The Israeli pro-peace group Peace Now released a report Wednesday saying West Bank settlements expanded more in 2008 than they had the previous year. The report said 1,257 new structures were built in settlements during 2008, compared to 800 in 2007, an increase of 57 percent.

The Palestinians demand a complete halt to settlement building in the West Bank during peace negotiations, saying their expansion is taking land they demand for an independent state.