The Associated Press reports: Syrian President Bashar Assad urged his military Wednesday to boost its fight against rebels, but his written call to arms only deepened a mystery over his whereabouts two weeks after a bomb penetrated his inner circle.

Assad has not spoken publicly since the July 18 bombing killed four of his top security officials — including his brother-in-law — during a rebel assault on the capital, Damascus. The president’s low profile has raised questions about whether he fears for his personal safety as the civil war escalates dramatically.

The United States called the Syrian president a coward for marshaling his forces from the pages of the army’s official magazine.

“We think it’s cowardly, quite frankly, to have a man hiding out of sight, exhorting his armed forces to continue to slaughter the civilians of his own country,” said U.S. State Department spokesman Patrick Ventrell.

Sausan Ghosheh, the spokeswoman for the U.N. mission in Syria, said Wednesday that international observers witnessed warplanes firing in Aleppo, Syria’s largest city, where intense fighting has been raging for 12 days.

Speaking to reporters in Damascus, Ghosheh said the situation in Aleppo was dire.

“Yesterday, for the first time, our observers saw firing from a fighter aircraft. We also now have confirmation that the opposition is in a position of having heavy weapons, including tanks,” she said, adding that for civilians, there “is a shortage of food, fuel, water and gas.”

The U.N.’s World Food Program said it was sending enough emergency food aid for 28,000 people in the city of 3 million. The U.N. has estimated that some 200,000 residents have fled Aleppo.