Egypt's ruling Muslim Brotherhood warned on Thursday that it will defend its headquarters as hundreds of its members gathered outside the building ahead of an opposition protest.

The Islamists were bussed in to stand guard outside the building in Cairo, where opposition activists who plan to hold a protest on Friday had previously clashed with Brotherhood members.

Syrian opposition leader Soheir Atassi of the Syrian National Coalition grouping said on Thursday she was rejoining the body a day after abruptly "freezing" her membership.

"The main reason I froze my participation is the failure of organizational work and the lack of professionalism," Atassi wrote on her Facebook page.

Palestinian President Mahmud Abbas on Thursday slammed violence against civilians, including Gaza rocket fire after two projectiles hit Israel as U.S. President Barack Obama visits.

"We condemn violence against civilians, whatever its source, including the firing of rockets," political adviser Nimr Hammad quoted Abbas as saying.

President Bashar Assad called the more than two-year deadly conflict in Syria a "battle of will and resistance," in remarks published in newspapers on Thursday.

"Today, all of Syria has been wounded," he was reported as saying on a visit the previous day to an educational center in the capital.

U.S. President Barack Obama on Thursday urged Israelis and Palestinians to get back to peace talks but offered no new ideas on how they might do so, essentially abandoning his previous support of the Palestinian demand for Israel to halt settlement activity before negotiations resume.

In remarks likely to disappoint, if not infuriate, the Palestinians, Obama said the United States continues to oppose the construction of Jewish housing on land claimed by the Palestinians but stressed that issues of disagreement between the two sides should not be used as an "excuse" to do nothing. He said there would be no point to negotiations if differences had to be resolved before they start.

Two rockets fired by militants in the Hamas-run Gaza Strip on Thursday hit southern Israel as U.S. President Barack Obama was visiting the Jewish state, police said.

"One exploded in the back yard of a house in Sderot, causing damage, and the second landed in a field," police spokesman Micky Rosenfeld told Agence France Presse, referring to a town very close to the Gaza border, which was visited by Obama on a previous trip in 2008 when he was a senator.

The number of Syrians seeking asylum in developed nations tripled last year, the U.N. refugee agency said Thursday, amid an eight-percent overall rise in people looking for a safe haven in rich countries.

Syrian asylum claims in 44 industrialized countries jumped to 24,800 from 8,400 in 2011, the year the civil war began.

Russia backtracked Wednesday over claims that Syrian rebels had used chemical weapons, saying the information still had to be checked.

The foreign ministry said on Tuesday it had information from Damascus the rebels had used chemical weapons in an attack that day in Aleppo province that Syria claimed killed 16 people.

U.S. President Barack Obama on Wednesday warned the Damascus regime it would be held accountable for any use of chemical weapons against civilians in Syria in a move which would spark an international response.

Speaking at a joint news conference with Israeli Prime Minister Benjamin Netanyahu in Jerusalem, Obama said the use of chemical agents against the Syrian people would be a "grave and tragic mistake" and a "game-changer."

Palestinian militants pitched a protest camp Wednesday on the site of a contested Jewish settlement, in an act of defiance as U.S. President Barack Obama began an historic visit.

Israel's plan to build in a strip of West Bank land outside Jerusalem called E1 has sparked a major international backlash, with experts saying it could wipe out hopes for the establishment of a viable Palestinian state.