After meeting with the British Foreign Secretary Philip Hammond in London on Saturday, US Secretary of State John Kerry said the Russian jets in Syria could pose a threat to America and its allied forces.
Kerry also asserted that Syrian President has to go, as there no future for him in Syria, but the timing of his departure needs to be decided through negotiation.
Kerry had this to say about Assad's departure "For the last year and a half we have said Assad has to go, but how long and what the modality is ...that's a decision that has to be made in the context of the Geneva process and negotiation."
A day before the talks, Russia moved a small number of fighter jets to a base in Syria, according to US officials.
"Clearly, the presence of aircraft with air-to-air combat capacity ... raises serious questions," Kerry said.
Russia had declared earlier that the aircraft are there to provide support for the Syrian regime against ISIS.
Since the invasion of Afghanistan by the Soviet forces ended, the Russian military expansion in Syria is considered to be the first major military operation outside of the former Soviet Union.
Philip Hammond said that Assad could not be part of Syria's future, but the date of his departure is not a matter of concern at the current time as much as reaching a political solution to end the Syrian war.
"The modality and timing has to be part of a political solution " he said.
On Sept. 9, Hommond had said Britain could accept Assad to remain in power during a transition period.
After the talks with his counterpart in London, Kerry affirmed the necessity of cooperation in finding a solution for the crisis in Syria.
"Both US and Britain agreed completely on the urgency of nations coming together in order to resolve this war that has gone on for much too long," said Hammond.
"So there's a lack of logic," Kerry said, for the Russians to say "they are bringing in more equipment to shore up Assad at the same time they say they are going after the militants."
"All of us join together in urging everybody to keep the calm," Kerry added.
John Kerry thinks that the Syrian war is what caused the refugees' crisis in the first place, therefore a compromise should be made to solve it.Russian planes carrying aid land in Syria
Kerry told reporters on Friday that the Pentagon would participate in discussions with Russia, but stopped short of elaborating exactly where, when and at what level talks will be held.
The four-year-long war in Syria has claimed the lives of hundreds of thousands while it displaced half of the pre-war 22 million population of the country internally and externally. At least 350,000 refugee have claimed asylum in the European countries since the war began in Syria in 2011.
According to the UNHCR, in a bigger humanitarian dilemma. Thousands of those refugees who are traveling illegally had drowned or died on the way to Europe.