President Barack Obama has ruled out deploying US ground troops in Syria and says military efforts alone cannot solve the country's problems.

"It would be a mistake for the United States, or Great Britain... to send in ground troops and overthrow the [Bashar al-] Assad regime," he told the BBC.

He also said he did not think so-called Islamic State would be defeated in his last nine months of office.

But he said: "We can slowly shrink the environment in which they operate."

Obama, who has been in the UK for a three-day visit, said Syria was a "heart-breaking situation of enormous complexity".

"I don't think there are any simple solutions," he said.

(BBC)