The US president and his Russian counterpart have expressed agreement in a telephone call on "the need to advance a political transition" and seek "new initiatives" to end the violence in Syria as soon as possible, the White House has said.

Barack Obama and Vladimir Putin welcome "substantive and constructive consultations" by Secretary of State John Kerry and Russian Foreign Minister Sergey Lavrov over a political transition in Syria, the White House said in a statement on Friday.

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The statement did not elaborate further on Friday's discussion between the two leaders on the Syria conflict.

Moscow and Washington have long been at odds over the fate of Syrian President Bashar al-Assad.

The US says he must go but Russia says his exit from power must not be a precondition for a negotiated settlement.

Obama and Putin also agreed to hold bilateral talks at the Group of Eight summit in Northern Ireland in June.

The US president also welcomed Russia's co-operation on international efforts to confront Iran's nuclear ambitions.

Fierce clashes

Meanwhile, a fierce battle on the outskirts of the northern city of Raqa, near the Turkish border, has killed dozens of Syrian troops and rebel fighters on Saturday, a watchdog reported.

"Fierce clashes pitting rebel fighters from several battalions against regular troops have raged since dawn on the outskirts of Raqa city... explosions could be heard in the city, and towers of smoke could be seen rising into the sky," said the UK-based Syrian Observatory for Human Rights.

A video posted online earlier in the day is said to show an explosion hitting buildings in the Damascus suburb of Daraya.

Activists have accused the Syrian government forces of being behind the attack.

United Nations is expected to announce next week that the number of Syrian refugees has passed one million

The area was reportedly targeted due to its proximity to the Mazzeh military base, which the rebels have seized.

In a joint press conference with Turkish Foreign Minister Ahmet Davutoglu on Friday, Kerry said they discussed how the international community can come together "in an effort to try to create a political transition" in Syria.

"We need to continue to work to make certain that the Assad regime makes a different set of choices," Kerry said.

Friday's diplomatic developments unfolded as Syrian government forces were engaged in fierce clashes with rebels, who attacked a police academy near the northern city of Aleppo.

The school, which activists say has been turned into a military base used to shell rebel-held neighbourhoods in the city and the surrounding countryside, has become a key front in the wider fight for Aleppo.

The Syrian state news agency said government troops defending the school had killed dozens of opposition fighters and destroyed five rebel vehicles.

Renewed clashes were also reported around Aleppo's landmark 12th century Umayyad Mosque in the walled Old City, which is a UNESCO World Heritage Site.

Meanwhile, the number of Syrian refugees has been rising rapidly and the UN says it is going to pass one million by next week.

The real numbers might be even bigger than that as the UN Refugee Agency does not take into account those that have not registered as refugees.

Source: Al Jazeera And Agencies