Dozens of prisoners were on the loose on Friday after militants attacked a prison in the Iraqi city of Tikrit, leaving at least 13 policemen dead, officials said.

The violence at the prison comes after al-Qaida's Iraqi front group announced a campaign to regain territory and said it aimed to help its jailed members escape.

Rebels unleashed an unprecedented barrage of mortar fire against troops in Aleppo after announcing a "decisive" battle for Syria's second city, residents and a watchdog say.

Shells crashed down at a steady rate and clashes were widespread, leaving layers of dust and smoke over Aleppo, according to the residents and the Syrian Observatory for Human Rights.

Israeli Prime Minister Benjamin Netanyahu drew the world a stark red line Thursday, warning that Iran could have a nuclear bomb in less than a year and demanding international action.

Wielding a red marker pen and a cartoonish diagram of a round bomb with a fizzing fuse, Netanyahu told the U.N. General Assembly that the international community must put a limit on Tehran's uranium enrichment.

Several thousand Syrian rebels on Thursday afternoon launched what they said would be a decisive battle for control of the strategic northern city of Aleppo.

"Tonight, Aleppo will be ours or we will be defeated," Abu Furat, a rebel commander, told AFP.

Syrian authorities on Thursday sent text messages over cell phones nationwide with a message for rebels fighting President Bashar Assad's regime: "Game over."

The messages signed by the Syrian Arab Army also urged the rebels to surrender their weapons and warned the countdown to evict foreign fighters has begun. The texts appear to be part of the regime's psychological battle against the rebels, but are highly unlikely to have any effect on fighters intent on toppling Assad.

Russia's U.N. Security Council veto is "just an excuse" for world powers not to intervene in Syria, but the regime is going to fall without their help, the chief of Syria's Muslim Brotherhood told AFP Thursday.

"Russia is just an excuse for the rest of the great powers not to topple (Syrian President Bashar Assad's) regime," said Mohammed Riyad al-Shaqfa, complaining of an international unwillingness to "get sucked into" the conflict in Syria.

Russian President Vladimir Putin on Thursday accused the West of pursuing policies that had destabilized states in the Arab world and now risked creating chaos in Syria.

"The most important thing is that our partners cannot stop themselves," news agencies quoted Putin as saying at his local Moscow residence at a meeting with local residents of the Ryazan region in central Russia.

German Chancellor Angela Merkel has canceled a planned trip to Tunisia next month, a spokesman said Thursday, amid reported security concerns over bloody unrest in the Arab world.

A spokesman from her office confirmed a report in the daily Financial Times Deutschland (FTD) that the German leader had axed the visit "by mutual agreement" with the Tunisian government.

Unidentified attackers blew up an oil pipeline in the northeast Syrian province of Hasaka on Thursday, after a car bomb attack on an army checkpoint near Aleppo overnight, a watchdog said.

The latest violence came after more than 300 people were killed nationwide on Wednesday in what the Syrian Observatory for Human Rights said was the bloodiest day of the 18-month conflict so far.

Egypt sees no reason to make changes to its peace treaty with Israel, presidential spokesman Yasser Ali said in statements carried Thursday by the state-owned paper Al-Ahram.

"There is no need for the moment to amend the Camp David agreement," said Ali who was accompanying President Mohammed Morsi in New York for the meetings of the U.N. General Assembly.