According to four people familiar with the discussions, the US has told Russia it is ready to take strong military action against Syria if President Bashar al-Assad uses chemical arms to recapture one of his country’s last rebel-held areas, reported Bloomberg.

Such a warning was made by US National Security Adviser John Bolton during his talk with his Russian counterpart, Nikolai Patrushev, at a Thursday meeting in Geneva, Switzerland.

The US-Russian talks in Geneva also addressed topics including the possible removal of American troops from a military base on the Syria-Iraq border, or their cooperation with Russian forces nearby, according to the people familiar with the talks. No agreement was reached on the conditions under which that could happen, they said.

The US also rejected a Russian proposal for oil sanctions on Iran to be suspended as part of a broader settlement in Syria, the people said.