A day after challenging Israelis to embrace peace with Palestinians, US President Barack Obama Friday will face scrutiny over his strategy on Syria during an overnight stay in Jordan.

Palestinians sour at Barack Obama's perceived failure to honour their historical struggle have invoked the US civil rights movement and South Africa's apartheid in a bid to win his sympathy.

In a powerful direct appeal to Israelis, President Barack Obama insisted that a two-state peace with the Palestinians could still be forged and is their only hope of true security.

The United States has found no evidence to support a Syrian government allegation that opposition rebels used chemical weapons in an attack this week, a US official said Thursday.

A hardline Islamist group claimed a rocket attack against southern Israel on Thursday, in a statement that condemned a historic visit by US President Barack Obama to the region.

In a powerful direct appeal to Israelis, President Barack Obama Thursday insisted a two-state peace with the Palestinians could still be forged and was their only hope of true security.

Palestinian president Mahmud Abbas on Thursday welcomed a speech to young Israelis in which US President Barack Obama appealed for a two-state peace with the Palestinians, a senior Palestinian official said.

Jailed Kurdish rebel chief Abdullah Ocalan called Thursday for a new ceasefire, telling his fighters to lay down their arms and withdraw from Turkish soil, raising hopes for an end to a three-decade conflict that has cost tens of thousands of lives.

The United States on Thursday welcomed a call from the jailed rebel leader of the Kurdistan Workers' Party (PKK) urging his fighters to lay down their arms, saying it was a "positive step."

Jailed Kurdish rebel chief Abdullah Ocalan called Thursday for a new ceasefire, telling his fighters to lay down their arms and withdraw from Turkish soil, raising hopes for an end to a three-decade conflict that has cost tens of thousands of lives.

The United Nations will investigate whether chemical weapons have been used in the Syria conflict, UN leader Ban Ki-Moon announced Thursday.

Iran's supreme leader on Thursday signalled openness for the first time to US offers to hold direct talks on his country's disputed nuclear drive, but voiced pessimism over the chances of a breakthrough.

Credit ratings agency Moody's said on Thursday it has downgraded Egypt's government bond ratings by one notch to Caa1 from B3, saying political instability had "significantly weakened" the economy.

US President Barack Obama used a major speech in Israel on Thursday to issue a new call on Syrian President Bashar al-Assad to step down so his country's "future can begin."

Iran will "annihilate" the Israeli cities of Tel Aviv and Haifa if it comes under attack by the Jewish state, supreme leader Ayatollah Ali Khamenei warned on Thursday.

US President Barack Obama insisted on Thursday a two-state solution was still viable, but disappointed his Palestinian hosts by failing to take a clear stance on freezing settlement activity.

Egypt's ruling Muslim Brotherhood warned on Thursday that it will defend its headquarters, as opposition activists planned a march on the building where they have previously clashed with the Islamists.

Palestinian president Mahmud Abbas on Thursday told US President Barack Obama there could be no talks with Israel without a freeze on settlement construction.

Two rockets fired by militants in the Hamas-run Gaza Strip on Thursday hit southern Israel, police said, sparking a top-level condemnation from visiting US President Barack Obama.

Iran will "annihilate" the Israeli cities of Tel Aviv and Haifa if it comes under attack by the Jewish state, the Islamic republic's supreme leader Ayatollah Ali Khamenei warned on Thursday.