Israeli President Shimon Peres has raised the possibility of an interfaith conference on peace during a recent encounter with Pope Francis in Rome, the presidency said on Thursday.

"The issue of a multi-faith conference was raised, and President Peres expressed his belief that Pope Francis can play an important role in progressing peace," the office of Peres informed Agence France Presse in a statement.

The United States warned Israel Thursday that continued settlement activity in east Jerusalem was "counterproductive" to efforts to reach a peace deal with the Palestinians.

Reacting to reports Israel is planning more than 1,000 new settler homes in east Jerusalem, State Department spokeswoman Jen Psaki called on both sides to take action to build confidence needed to build a lasting peace.

Attacks in Iraq, including a spate of bombings in Baghdad, killed 26 people on Thursday, officials said, the latest in a spike in violence that has sparked fears of all-out sectarian war.

The unrest pushed the overall number of people killed so far in May above 600, by far the deadliest month in Iraq in at least a year, according to Agence France Presse figures based on information from security and medical officials.

Syria's main opposition group said Thursday it will not take part in proposed U.S.-Russia peace talks while key allies of President Bashar Assad's regime are waging war alongside government forces.

"The National Coalition will not take part in any international conference or any such efforts so long as the militias of Iran and Hizbullah continue their invasion of Syria," the opposition's acting chief George Sabra told reporters in Istanbul.

Bahrain has urged its citizens not to travel to Syria to fight alongside rebels ranged against government forces after a Bahraini youth was killed there in battle, local press reported Thursday.

"Supporting the right of the Syrian people to self defense should be done through the efforts of the international community... in a way that benefits our Syrian brothers," said interior minister Rashid bin Abdullah al-Khalifa, according to press reports.

Russia has delivered sophisticated air defense missiles to Syria, President Bashar Assad has implied in an interview to be aired Thursday on Hizbullah's al-Manar television, the network said.

Al-Manar said in a statement that when asked about the promised delivery of the S-300 surface-to-air missiles, Assad replied: "All the agreements with Russia will be honored and some already have been recently."

Syria's opposition National Coalition launched an urgent appeal on Thursday to rescue 1,000 wounded civilians from the town of Qusayr, which government troops and Hizbullah fighters are battling to retake from rebels.

"Qusayr has been under constant bombardment," a statement said, and a "large number of civilians living in the area have been injured due to the assault launched over two weeks ago on the city."

Renewed fighting between two rival Arab tribes in Sudan's Darfur region over access to pasture has killed 64 people, police said in a statement late on Wednesday.

Dozens more were wounded in the fighting between the Beni Halba and Gemir tribes, South Darfur police said.

Russian Foreign Minister Sergei Lavrov on Thursday accused the Syrian opposition of seeking to disrupt plans for a peace conference by putting forward unrealistic demands.

"We are under the impression that the National Coalition and its regional sponsors are doing everything so as not to allow the start of the political process and achieve military intervention in Syria through any means possible," Lavrov told reporters.

Israel's decision to build 1,000 new settler homes in annexed east Jerusalem is "destroying" efforts by Washington's top diplomat to revive the peace process, a Palestinian official said on Thursday.

"We consider the recent decision of the Israeli government to build a thousand homes in east Jerusalem as effectively destroying the efforts of (U.S. Secretary of State) Kerry," top Palestinian negotiator Saeb Erakat told Agence France Presse.