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JERUSALEM (AP) — Eager to reassure an anxious ally, President Barack Obama on Wednesday promised to work closely with Israel and do whatever is necessary to keep Iran from obtaining nuclear arms, "the world's worst weapons." He also pledged to investigate whether chemical weapons were used this week in neighboring Syria's two-year-old civil war.

Obama, after meeting with Israeli Prime Minister Benjamin Netanyahu, said of Iran's nuclear ambitions: "We prefer to resolve this diplomatically, and there is still time to do so." But he added that "all options are on the table" if diplomacy falls short."The question is, will Iranian leadership seize that opportunity," he added. The president said Iran's past behavior indicates that "we can't even trust yet, much less verify."

Netanyahu, at Obama's side for a joint news conference, said that while he appreciated U.S. efforts to thwart Iran's pursuit of nuclear weapons through diplomacy and sanctions, those tools "must be augmented by a clear and credible threat of military action."

"I am absolutely convinced that the president is determined to prevent Iran from getting nuclear weapons," Netanyahu said. "I appreciate that. 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."

The Israeli leader said that he and Obama agree that it would take Iran about a year to manufacture a nuclear weapon if it tries to do so.

Obama said there is "not a lot of light, a lot of daylight" between the two leaders in intelligence assessments about Iran, and Netanyahu concurred.

Although preventing Iran from developing a nuclear weapon is a priority of both Israel and the United States, Netanyahu and Obama have differed on precisely how to achieve that.

Israel repeatedly has threatened to take military action should Iran appear to be on the verge of obtaining a bomb. The U.S. has pushed for more time to allow diplomacy and economic penalties to run their course, though Obama insists military action is an option.

Obama noted the difficulty of finding a path forward in the broader quest for Mideast peace, acknowledging that in recent years "we haven't gone forward, we haven't seen the kind of progress that we would like to see."

The president said he came to the region principally to listen and hopes to return home with a better understanding of the constraints and "how the U.S. can play a constructive role."

"This is a really hard problem," he said.