President Obama's trip to the Middle East is primarily about how to find a path to peace between Israelis and Palestinians. But the war in Syria, where Israel is increasingly concerned about Iran's involvement and the growing calls to arm the Syrian rebels, are issues likely to be discussed during Obama's trip.
With President Assad's forces still controlling Syrian air space, rebels want the United States to give them the weapons they say they need to finish the fight.
"When we are denied weapons, we don't have the capacity to defend our families and the killings will continue," said Salim Idrss of the Free Syrian Army.
But arming Assad opponents has its own risks, says U.S. Institute of Peace
analyst Steve Heydemann.
"There continues to be concern about the political risks involved if we should ever - even 20 years from now - read that the weapons provided by the United States played a role in an attack on Americans," he said.
Israel is also concerned about arming Syrian rebels.
Although Syria, under Bashar al-Assad, has been an ally of Iran and of Hezbollah in Lebanon, the Israeli-Syrian border has been calm for years.
"There is concern in Israel, for example, that sending arms to the Syrian opposition will be equipping groups that could some day use them against Israel," said Heydemann. "There is concern that if the Iranian-Syrian-Hezbollah axis is broken, Iran will feel more endangered, more threatened, and could in fact be more inclined to push its nuclear program more quickly toward a nuclear-weapons capability."
Israeli Prime Minister Benjamin Netanyahu does not believe U.S.-led sanctions will end Iran's nuclear threat. And Washington appears to have no leverage over President Mahmoud Ahmadinejad, says Johns Hopkins University professor Ruth Wedgwood.
"Some of this may be Ahmadinejad trying to enhance his own national stature because he's not as well-liked as before within Iran. But it's not a time when the US appears to have any influence," she said.
Josh Earnest, a White House spokesman, says President Obama understands Israel's concerns.
"Israel's neighborhood, if you will, is undergoing a pretty severe transition, and there's crisis, and it's important for the people of Israel to understand that the American people stand with them in that time of crisis and that we're going to be there to protect them and work with them to ensure their security," he said.
As for arming the Syrian rebels, Secretary of State John Kerry has said the U.S. will provide direct assistance to the fighters, but no weapons.
Syrian rebels say the war will continue until its allies move to match the weapons President Assad is receiving from Iran and Russia.