Turkish Prime Minister Tayyip Erdogan and U.S. President Barack Obama discussed how they could work together to speed up political transition in Syria during a telephone call, Erdogan's office said.
Erdogan, who once enjoyed close ties with Syrian President Bashar Assad, has become one of his fiercest critics and has demanded he step down in the face of a 16-month-old uprising in which thousands of civilians have died.
"In the talks, they took up the co-ordination of efforts to accelerate the process of political transition in Syria, including Bashar Assad leaving the administration and the meeting of the Syrian people's legitimate demands," a statement from Erdogan's office said.
The phone call took place on Monday and Turkish media reports said Erdogan and Obama spoke for 36 minutes.
"The two leaders expressed their growing concern about the worsening human conditions in Syria because of the Syrian regime's attacks targeting its own people and the regime's savagery, most recently seen in Aleppo," it said.
Obama and Erdogan also discussed the need to work together to assist civilians trying to escape the violence in Syria.
There are about 44,000 Syrian refugees in Turkey and there are concerns that the offensive by Assad's army in the northern city of Aleppo could lead to increasing numbers.
"Prime Minister Erdogan and President Obama agreed on the co-ordination of efforts to help Syrians forced to flee to Turkey and neighboring countries," the statement said.
Meanwhile, Syrian rebels attacked the ruling Baath party office and the military hospital in Aleppo, northern Syria, on Tuesday, as fighting continued for the fourth consecutive day.
"Our rebels managed to attack the Baath party office, the military hospital as well as the military court in the area of al-Mahfaza," Abu Omar al-Halabi, a Free Syrian Army commander, told dpa from Aleppo.
He said that six rebels had been killed in the clashes, while some 15 members of the government forces, including a high-ranking officer, defected to the opposition ranks near the military court.
Al-Halabi said the rebels were now controlling 60 percent of Aleppo, Syria's commercial capital, but that fighting was gripping the Salah ad-Din and al-Sukari areas.
"The regime forces are cowards, they are not moving on the ground but they are shelling rebel-held areas in Aleppo with rocket launchers, heavy artillery and helicopters," he said.
In the capital Damascus, activist Haytham al-Abdullah told dpa that government forces had shelled areas at dawn in and around the Palestinian refugee camp in Yarmouk, located inside the city.
The London-based Syrian Observatory for Human Rights said Monday's death toll reached 100, most of which were in Aleppo and the central province of Homs.
In Cairo, Syrian opposition members are scheduled to meet Tuesday to discuss ways of forming a transitional government once President Assad is no longer in power.
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