President Barack Obama fought back against critics of his foreign policy on Wednesday, by insisting a US reliance on diplomacy over military intervention was working, pledging to ramp up support for Syria's opposition.
Obama was speaking to cadets at West Point Military Academy and used the platform to state that his "bottom line" was that "America must always lead on the world stage."
ITV News' Washington correspondent Robert Moore reports:
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Many police are said to have been seriously wounded in the attack which may have been targeted at them, officials said.
Syrian government forces are continuing a push for total control of Aleppo, while a reported 20,000 civilians left the city on Saturday.
Rex Tillerson is president of Exxon Mobil and has close business links to Russian President Vladimir Putin.