JERUSALEM (AP) ― Seeking a fresh start to a strained relationship, President Barack Obama and Israeli Prime Minister Benjamin Netanyahu on Wednesday demonstrated solidarity on the key issues that have stirred tensions between them. The U.S. president vowed he would do “what is necessary” to prevent Iran from obtaining a nuclear weapon, while Netanyahu reaffirmed that his newly formed government seeks a two-state solution to Israel’s decades-long dispute with the Palestinians.

Obama, in Israel for the first time in his presidency, also pledged to investigate reports that Syria had used chemical weapons for the first time in its two-year civil war. And he sternly warned Syrian leader Bashar Assad that use of such weapons would be a “game-changer,” one that could potentially draw the U.S. military into the conflict for the first time. 

“The Assad regime must understand that they will be held accountable for the use of chemical weapons or their transfer to terrorists,” Obama said, standing alongside Netanyahu at a nighttime news conference.

Expectations were low for a breakthrough during Obama’s visit on any of the major issues roiling the region. Instead, the president was focused on reassuring anxious Israelis that he is committed to their security, and on resetting his rocky relationship with Netanyahu. The two leaders have been at odds over Israeli settlements and Iran’s disputed nuclear programs, and Netanyahu famously lectured Obama in front of the media in the Oval Office on Israel’s right to defend himself.

Compared with past encounters, there was a noticeable lack of uneasiness Wednesday, the first time the two leaders have met publicly after both survived elections that will leave them stuck with each other for the foreseeable future. They traded jokes throughout a day of side-by-side appearances. And they repeatedly referred to each other by their first names, Obama calling his Israeli counterpart by his nickname, “Bibi.”

On Iran in particular, the two leaders sought to show they were united in their desire to prevent the Islamic republic from developing what Obama called “the world’s worst weapons.”

Although preventing Iran from developing a nuclear weapon is a priority of both countries, Netanyahu and Obama have differed on precisely how to achieve that goal. Israel repeatedly has threatened to take military action should Iran appear to be on the verge of obtaining a bomb, while the U.S. has pushed for more time to allow diplomacy and economic penalties to run their course.

Obama said he continues to prefer a diplomatic solution and sees time to achieve it. Whether that works, he said, will depend on whether Iran’s leaders “seize that opportunity.”

Although Obama did not promise that the United States would act militarily against Iran if Israel decided that must be done, he offered an explicit endorsement for Israel to take whatever unilateral measures it deems necessary to guard against the threat.

“Each country has to make its own decisions when it comes to the awesome decision to engage in any kind of military action, and Israel is differently situated than the United States,” he said. “I would not expect that the prime minister would make a decision about his country’s security and defer that to any another country any more than the United States would defer our decisions about what was important for our national security.”

Netanyahu strongly backed Obama’s efforts, saying he was “absolutely convinced” the U.S. is determined to prevent Iran from getting nuclear weapons.

“I appreciate the fact that the president has reaffirmed, more than any other president, Israel’s right and duty to defend itself by itself against any threat,” he said.

The Israeli leader also said that he and Obama agree that it would take Iran about a year to manufacture a nuclear weapon. Obama said there is “not a lot of light, a lot of daylight” between the two leaders in intelligence assessments about Iran.

The two leaders also spoke firmly about the need to pursue a peace deal between Israel and the Palestinians, an effort that was stymied during Obama’s first term. The president, who arrived in Israel without a clear pathway for jumpstarting talks, acknowledged that in recent years, “we haven’t gone forward, we haven’t seen the kind of progress that we would like to see.”

Netanyahu, for his part, said he was willing to set aside preconditions in future talks with the Palestinians, adding that it was time to “turn a page in our relations.”

But they avoided tackling any of the intractable issues that have derailed the peace process, including Israeli settlement building and the status of Jerusalem. Obama promised to talk about peace efforts more expansively Thursday during a speech to Israeli youth.

He also was making a quick trip to the West Bank Thursday to meet with Palestinian Authority President Mahmoud Abbas. Obama planned to visit a youth center in Ramallah before heading back to Jerusalem to deliver a speech and attend a formal dinner with Peres.

He will also travel to Jordan later in the week, a stop aimed at shoring up government reforms by the important U.S. ally and pledging American support in dealing with the 450,000 Syrian refugees that have flooded over the border.

On another troubling issue in the Syria fighting, Obama said the U.S. is investigating whether chemical weapons have been used there. Both the Assad government and Syrian rebels have accused each other of using chemical weapons in an attack on Tuesday.

“Once you let that genie out of the bottle, then you are looking potentially at even more horrific scenes than we have already seen in Syria,” Obama said. “And the international community has to act on that information.”

Obama was greeted warmly upon his arrival in Israel Wednesday following an overnight flight from Washington. Netanyahu and Israeli President Shimon Peres met him at the steps of Air Force One as U.S. and Israeli flags waved on a breezy, sun-splashed afternoon.

During an elaborate welcome ceremony at Tel Aviv’s airport, the Israeli leaders lavished praise on Obama, with Netanyahu calling the U.S. president his “cherished guest” and Peres saying he was a “historic friend of Israel.” Obama responded in kind, saying he and his counterparts “share a vision of Israel at peace with its neighbors.”

Seeking to underscore U.S. military cooperation with Israel, Obama viewed an Iron Dome battery that was transported to the airport for his arrival. The U.S. has invested more than $275 million into the missile defense system and plans to spend another $211 million on it this year. U.S. and Israeli officials credit the Iron Dome with preventing numerous rocket attacks from neighboring Palestinian territories.

Obama also announced Wednesday that the U.S. and Israel would start talks soon on a new, 10-year security cooperation package to replace one that expires in 2017.

While Israel warmly greeted Obama, Palestinians held several small protests. In Gaza, demonstrators burned Obama posters and U.S. flags, accusing the U.S. of being unfairly biased toward Israel. In the West Bank, about 200 activists erected tents in an area just outside Jerusalem to draw attention to Israel’s policy of settlement building.