He gave no details, but media reports say the US Navy is strengthening its presence in the eastern Mediterranean.

On Friday, President Barack Obama said fresh allegations of chemical weapons use by the Syrian government this week was of "grave concern". Syria's main ally Russia said there was evidence rebels were behind the attack. The Syrian opposition, however, has said hundreds died in a government assault on the outskirts of Damascus on Wednesday.

Despite calls from many different countries, there is no sign yet that the Syrian authorities will allow a UN inspection team to visit to investigate the claims. The UN's disarmament chief, Angela Kane, is due to arrive in Damascus on Saturday to push for access to the site. UN Secretary General Ban Ki-moon said he is determined to "conduct a thorough, impartial and prompt investigation" into the events. Unverified footage shows civilians - many of them children - dead or suffering from what appear to be horrific symptoms as a result of the attack. [Link]