Updated

The leaders of Iran and Syria reaffirmed their support for "Palestinian resistance" on Tuesday, a defiant message to the U.S. and its Mideast allies who are uneasy over Washington's efforts to forge closer ties with the hard-line government in Tehran.

Iranian President Mahmoud Ahmadinejad was expected to meet with the chiefs of Hamas and other Damascus-based Palestinian radical groups during his visit to Syria, said Khaled Abdul-Majid of one of the groups, the Popular Struggle Front. Iran is a strong supporter of Islamic militants in the region, including Hamas and Lebanon's Hezbollah.

Ahmadinejad's visit to Syria comes as the U.S. is trying to improve strained ties with the two longtime adversaries. Two U.S. envoys, Jeffrey Feltman and Daniel Shapiro, left Washington on Tuesday for Syria for their second visit since March to explore ways to ease tensions between the United States and Syria, the State Department said.

But Ahmadinejad and his top Arab ally Syrian President Bashar Assad made little mention of American outreach as they sat together at a press conference following their talks.

The hard-line Iranian leader said the two countries' alliance was achieving "victories" in preventing "the big powers' offensive to dominate the region."

"Syria and Iran have been from the very beginning united and in agreement to stand on the side of the Palestinian resistance," Ahmadinejad said. "They will continue to do so. We see that the resistance will continue until all occupied territories are liberated."

Ahmadinejad and other Iranian officials have been sending mixed messages in response to President Barack Obama's calls for dialogue — at times taking a moderate tone, only to fall back on a tough line.

U.S. Defense Secretary Robert Gates, who is visiting the Middle East, said Tuesday the U.S. is still waiting to see how the Iranians respond to Obama's outreach, but so far the rhetoric from Ahmadinejad has been "not very encouraging."

Gates sought to reassure U.S. Arab allies, who are worried that their rival Iran will be boosted by a U.S. dialogue. He also said a "grand bargain" between Tehran and Washington was unlikely.

There has been widespread speculation in the Middle East that the Obama administration would try to forge a "grand bargain" with Iran, in which Washington would press Israel for concessions in the peace process with the Palestinians in exchange for Tehran rolling back its nuclear program.

"The United States will be very open and transparent about these contacts, and we will keep our friends informed of what is going on so nobody gets surprised," Gates said at a news conference in Egypt before heading to the Saudi capital.

The U.S. overtures to Iran are raising concerns among its Arab allies like Egypt and Saudi Arabia, as well as Israel. They fear Iran is trying to spread its influence across the Middle East, with its support of Hamas, Hezbollah and other militant groups.

Arab diplomats who met in Cairo Tuesday with the State Department's new special envoy for the Persian Gulf, Dennis Ross, said they voiced those concerns.

"Some of what he heard was more than just grievances. They warned that Washington should be careful not to be so mild to Iran," said one diplomat who attended one of these encounters. He spoke on condition of anonymity because of the sensitivity of the subject.

Egyptian Foreign Minister Ahmed Aboul-Gheit expressed similar concerns on Monday.

"Iran's behavior in the region is negative in many aspects and does not help in advancing security, stability and peace," the state-run Middle East News Agency quoted Aboul Gheit as telling Ross.

Israeli Prime Minister Benjamin Netanyahu is due to meet Obama later this month at the White House for their first meeting since each leader took office earlier this year. Netanyahu is expected to come under pressure to publicly accept the principle of a Palestinian state, a step he has avoided amid U.S. attempts to revive the peace process.

Netanyahu is expected in turn to push for a tough U.S. stance on Iran. Israel argues that progress in peace with the Palestinians can't happen unless Iran is reined in.

Hamas' top political leader Khaled Mashaal, who is based in Syria, was quoted by the New York Times Tuesday as saying that Hamas is willing to support a two-state solution. But he also said Hamas would not renounce violence against Israel or recognize the Jewish state.