JERUSALEM: Barack Obama on Wednesday began his first presidential visit to Israel, pledging an "eternal" alliance with the Jewish state as it faces the Iranian nuclear threat and perilous change in the Middle East.

"The United States is proud to stand with you as your strongest ally and your greatest friend," Obama said at a lavish welcoming ceremony at Tel Aviv's Ben Gurion airport after Air Force One rolled to a halt to a peal of military trumpets.

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 of how to handle Iran's nuclear drive, the growing threat from Syria and peace with the Palestinians.

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

The president's opening message was clearly one of reassurance, aimed at offsetting persistent Israeli scepticism over his strategy for confronting Iran.

"Our alliance is eternal, it is for ever," he said on an unusually hot spring day as hundreds of US and Israeli flags snapped loudly in the wind.

"The United States is proud to stand with you as your strongest ally and your greatest friend," he declared, saying America's national security interests mandated a strong defence of Israel.

Before leaving the airport, the US leader came face-to-face with Israel's preoccupation with security, visiting a mobile battery of the US-funded Iron Dome missile defence system.

Then he was choppered up to Jerusalem in Marine One where, after a brief stop at the King David Hotel, he was driven to Peres's residence and 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.

After a quick tour of Peres's garden, the two got down to business with an hour-long meeting which Obama later said had focused on Iran, the peace process and the turmoil in the Middle East.

Peres flagged Iran and Syria as top concerns, warning that Damascus's chemical weapons stockpile must not be allowed to fall into the wrong hands.

"Fortunately the Syrian nuclear capacity was destroyed but unfortunately the arsenal of chemical weapons remain.

We cannot allow those weapons to fall into terrorists' hands -- it could lead to an epic tragedy," he said at a

joint news conference.

Fears over Syria's chemical weapons peaked on Tuesday following claims that chemical agents had been used in a deadly attack in the northern province of Aleppo, although it was not immediately clear whether regime forces or rebels were responsible.

So far, Washington said there is no evidence that chemical weapons were actually used in a move which the Obama administration has warned would be crossing a "red line" and result in unspecified US action.

Peres said the biggest danger remained Iran's nuclear programme, which Israel and much of the West believes is a guise for a weapons drive -- a charge Tehran denies.

"The greatest danger is a nuclear Iran... We trust your policy which calls first to try by non-military means with a clear statement that there are other options on the table," he said, expressing a confidence which is rarely expressed by Israeli officials.

Obama was quickly shuttled to Netanyahu's official residence which is several streets away for a working meeting at which Iran was to be a central issue.

But it looked unlikely the two would narrow their differences over the point of no return.

Obama has said Iran will not be able to build a nuclear weapon for "over a year or so" but Netanyahu believes it could have the capacity to produce a bomb within months, and questions whether sanctions will change Tehran's calculations.

The two are also expected to discuss the relationship with the Palestinians with Obama expected to warn that

settlement building undercuts the chances of resuming talks.

Obama's arrival comes after a two-and-a-half year deadlock in direct talks which broke down just weeks after

they were personally launched by the US leader in September 2010.

During his three-day visit, Obama will hold talks in Ramallah with Palestinian president Mahmud Abbas, although he has made clear that he is here to listen to both sides rather than launch any new peace initiative.

He was expected to tell the Palestinian leader that initiatives like seeking recognition as a UN state were counterproductive.

Disillusioned by the failure of Obama's first-term peace efforts, the Palestinians are hoping he will help broker the release of more than 1,000 prisoners held by Israel and also free up $700 million in blocked US aid.

Among the US delegation is newly-appointed Secretary of State John Kerry, who will travel with Obama to Jordan on Friday but return to Israel on Saturday "to review the results of the president's visit following his stops in Ramallah and Amman," a State Department official told AFP.