US President Barack Obama warned Sunday that it would be a "mistake" to send Western troops into Syria to overthrow the regime of President Bashar al-Assad.
In an interview with the BBC, he said the United States would continue strikes against the Islamic State group while continuing efforts to broker a transition deal between the Assad regime and his moderate Syrian opponents.
"Syria has been a heart-breaking situation of enormous complexity, and I don't think there are any simple solutions," Obama said during his visit to London which ended Sunday.
"It would be a mistake for the United States, or Great Britain, or a combination of Western states to send in ground troops and overthrow the Assad regime.
"But I do believe that we can apply international pressure to all the parties, including Russia and Iran, who, essentially, are propping up Assad, as well as those moderate oppositions that exist and may be fighting inside of Syria, to sit down at the table and try to broker a transition.
"Now, that's difficult, and in the interim, we continue to strike ISIL targets in places like Raqqa, and to try to isolate those portions of the country, and lock down those portions of the country that are sending foreign fighters into Europe."
At least 30 civilians were killed Saturday in fighting in areas across Syria, threatening an eight-week-old truce as peace talks in Geneva remain stalled.
The truce, brokered by Russia and the United States, had raised hopes that United Nations-backed talks in Geneva this month will help resolve the five-year conflict.
"There's going to be a military component to this, to ensure that... we're also engaging in the counter-terrorism activities that are necessary," Obama said.
"But in order for us to solve the long-term problems in Syria, a military solution alone -- and certainly us deploying ground troops -- is not going to bring that about."
More than 270,000 people have been killed since Syria's conflict broke out in 2011.