A number of Western countries, including the United Kingdom, have long been vocally supportive of the Syrian opposition and insisted on removing Assad from power.
"There has always been the idea that there would be a political transition," the source said, answering a question on whether Assad could remain during a transition period, explaining that Cameron would not demand his immediate resignation.
Syria has been in a state of civil war since 2011. The country’s government is fighting a number of opposition forces, as well as radical Islamist militant organizations, including the Nusra Front and ISIL.
ISIL militants have seized large territories in the country and in the neighboring Iraq, and has been spreading its influence in the Middle East and African countries.