DUBAI, United Arab Emirates — President Bush wraps up a weeklong tour of the Middle East today, leaving many political observers mystified as to the purpose of the visit and doubtful that he made inroads on his campaigns for Arab-Israeli peace and isolation for Iran.

Bush is heading back to Washington mostly empty-handed, said several analysts and politicians throughout the region. Arab critics deemed Bush's peace efforts unrealistic, his anti-Iran tirades dangerous, his praise of authoritarian governments disappointing and his defense of civil liberties ironic.

"There is no credibility to his words after what the region saw during his presidency," said Mohamed Fayek, the Cairo, Egypt-based director of the nonprofit Arab Organization for Human Rights.

Fayek cited the war in Iraq, the prison camp in Guantanamo Bay, Cuba, and the Abu Ghraib prisoner abuse scandal.

"American policy threw the region off-balance and destabilized it," he said. "The visit caused deep disappointment. I don't see any results."

The challenges were evident yesterday. The Israeli military carried out an operation in Gaza that killed at least 18 Palestinians, including the 24-year-old son of Hamas leader Mahmoud Zahar, in the most violent day since the militant group seized control last year. Separately, a Palestinian sniper killed a young farmer from Ecuador who was working on an Israeli kibbutz near the border with Gaza.

Palestinians warned that the military raid could sour their talks with Israelis and undermine the momentum from Bush's visit to lead both parties back to the negotiating table.

"Skepticism on all sides is enormous," said Nicholas Pelham, a Jerusalem-based analyst with the International Crisis Group.

In Lebanon, an explosion targeting an armored U.S. Embassy vehicle in Beirut killed four Lebanese and injured others in the first assault on the U.S. diplomatic mission there since the 1980s. An American bystander was among the wounded, according to news reports. U.S. Secretary of State Condoleezza Rice called the incident a terrorist attack.

In another potential setback, Bush received a noncommittal response from the Saudi government to his request for increased oil production to reduce world oil prices. Saudi Oil Minister Ali Naimi insisted production would increase only "when the market justifies it."

Meanwhile, Bush didn't back down on his warnings to Iran, which he has lambasted at nearly every stop on his eight-day journey. He reiterated in Saudi Arabia that a military option wasn't out of the question, though he emphasized that he'd like to find a diplomatic solution to Iran's pursuit of a nuclear program and alleged funding of militants in Lebanon, Afghanistan, Iraq and the Palestinian territories.

However, many Gulf countries appear to be moving closer to Iran over Washington's objections.

"I guess the visit was just about making sure the Gulf doesn't slip away toward Iran," said Ghanim al-Najjar, the director of the Center for Strategic and Future Studies at Kuwait University. "All these issues will just stay on the surface because there is no environment to support action against Iran.

"Everything will stay on the level of rhetoric rather than reality."

The only comment that won Bush praise in the Arab press was his call for Israel to end "the occupation that began in 1967." But he quickly lost favor by holding up Israel as a regional example and defending embattled Israeli Prime Minister Ehud Olmert.