President Barack Obama Wednesday accepted Israel would not cede its right to confront Iran's nuclear threat to the United States, seeking to assuage anxiety over his commitment to the Jewish state.

Obama, on his debut trip to Israel as president, also warned Syria would face international action if it used chemical weapons in its civil war and admitted he could have been more "deft" in Israeli-Palestinian peace efforts.

All the tension and apparent mistrust that stained some previous encounters between Obama and Israeli Prime Minister Benjamin Netanyahu seemed to have dissolved when the leaders emerged from two hours of talks.

"Each country has to make its own decisions when it comes to the awesome decision to engage in any kind of military action," Obama said, when asked if he had told Netanyahu to be more patient before striking Iran.

"Israel is differently situated than the United States, and I would not expect that the prime minister would make a decision about his country's security and defer that to any other country."

Washington has worried that Netanyahu's hawkish rhetoric on Iran and warnings it could get most of the way to a nuclear bomb within months -- a shorter timeline than Washington's -- has sparked fears of an Israeli strike.

Netanyahu appeared moved by Obama's remarks, and delighted when the president also said Washington would enter talks to renew a multi-billion dollar military aid package for Israel after it expires in 2017.

"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," Netanyahu said.

Still, it did not appear that the men, who called one another "Barack" and "Bibi," managed to reconcile differing timelines over the point at which Iran would reach the point of no return and build a nuclear weapon.

Obama also insisted there was more time for diplomacy, backed by stringent sanctions to make Iran forgo its nuclear program, saying it was important to test the proposition that non-military means could work.

"The question is, will Iranian leadership seize that opportunity? Will they walk through that door?"

Earlier, Obama, who worried many Israelis when he told the Muslim world in his first term that he wanted a "new beginning" with Islam, went out of his way to affirm respect for the Jewish state and its defense.

After Air Force One touched down in Tel Aviv, Obama said the US-Israel alliance was "eternal, it is for ever," as hundreds of US and Israeli flags snapped in the wind.

"It's good to be back in The Land (Israel)," Obama said in Hebrew after being greeted on the red carpet by Netanyahu and President Shimon Peres.

The long-awaited visit, the first foreign tour of Obama's second term, comes just days after the installation of a new rightwing Israeli government which faces key challenges on Iran, Syria and the Palestinians.

Obama first headed to Peres's residence and was met by a troupe of flag-waving children, five of whom serenaded him with a rendition of the hit-musical number "Tomorrow" in Hebrew, English and Arabic.

Obama also issued a stark warning to Syria about using chemical weapons against its civilians, saying it would be a "grave and tragic mistake" and a "game-changer."

"The Assad regime must understand they will be held accountable," he said after the regime of Bashar al-Assad traded accusations with rebel forces over the use of chemical agents in an attack in the northern province of Aleppo which killed 31.

Washington says it has seen no evidence that such weapons were used, but Obama said he was "deeply sceptical" of any claim that opposition forces were involved.

Peres also warned about chemical arms falling into the wrong hands. "We cannot allow those weapons to fall into terrorists' hands -- it could lead to an epic tragedy," he said.

Obama's arrival comes after a two-and-a-half year deadlock in peace talks between Israel and the Palestinians, although Netanyahu insisted that his newly-inaugurated government remained committed to the two-state solution.

"Israel remains committed to the solution of two states for two peoples."

Obama will hold talks in Ramallah with Palestinian president Mahmud Abbas at 0900 GMT on Thursday, although he has made clear that he is here "to listen" to both sides rather than launch any new peace initiative.

He defended his failed peace bid in his first term which started with rousing promises to act, but foundered on an Israeli refusal to halt settlement activity and political divisions among Palestinians.

"I'm absolutely sure that there are a host of things that I could have done that would have been more deft and, you know, would have created better optics. But ultimately, this is a really hard problem," Obama said.

"It is a hard slog to work through all of these issues."

The Palestinians are hoping Obama will help broker the release of more than 1,000 prisoners held by Israel and also free up $700 million in blocked US aid.