The United States on Wednesday condemned Syria's use of attack helicopters in its civil conflict as "another indication of the depth of depravity" of the regime of President Bashar Assad.

White House spokesman Jay Carney issued the reaction aboard Air Force One following reports that helicopter gunships strafed several neighborhoods in Aleppo, Syria's commercial capital.

Russia on Wednesday lashed out at the United States for backing the armed opposition to the Syrian regime, saying Washington's failure to condemn the July 18 blast that killed top security officials meant it was justifying terror.

"This is quite an awful position, I cannot even find the words to make clear how we feel," Lavrov told reporters. "This is directly justifying terrorism. How can this be understood?"

"The United States of America" has become entrenched as one of the most frequently printed phrases in the modern era of written English, a study of 500 years of language evolution has shown.

Among the top dozen phrases most-printed in books every year, this one stands out from the other most popular five-word sentence components like "at the end of the", "as a result of the" or "on the part of the".

The United States is stepping up support for the Syrian opposition amid signs events in the 16-month uprising are moving faster on the ground, Secretary of State Hillary Clinton said Tuesday.

After failing to win a U.N. Security Council resolution on Syria after Russia and China imposed their vetoes, the United States is working outside the council to send "a clear message of support for the opposition," she said.

Gaps in U.S. intelligence have hampered Washington's efforts to speed the ouster of Syrian President Bashar Assad and develop a clear understanding of opposition forces inside the country, the Washington Post reported Tuesday.

Citing interviews with U.S. and foreign intelligence officials, the daily reported that U.S. spy agencies in recent months have expanded their efforts to gather intelligence on rebel forces and Assad's regime.

U.S. President Barack Obama warned Syrian leader Bashar Assad on Monday not to make the "tragic mistake" of turning to his stockpile of chemical weapons.

Assad's beleaguered regime had earlier threatened to unleash the weapons if Syria faced international military intervention, although it vowed not to turn them against its own civilians.

A top U.S. official said on Sunday that Washington has given $100 million in aid to Jordan to help host tens of thousands of Syrians who have fled the unrest back home and taken refuge in the kingdom.

U.S. ambassador to Jordan, E. Jones, said that the U.S. aid will also help Jordan meet its growing energy needs in light of the repeated cut-offs occurring from unstable gas supplies from Egypt.

Police in Aurora, Colorado, early Sunday dismissed suspicions that another person helped James Holmes prepared the massacre at a movie theater that left 12 people dead.

"There are multiple unconfirmed and inaccurate news reports about a second suspect," police spokeswoman Cassidee Carson said in a statement.

A U.S. military fighter jet crashed into the sea off northern Japan on Sunday and its solo pilot was waiting for rescue at sea after ejecting, the coast guard said.

"The F-16 jet crashed some 470 nautical miles northeast of Nemuro" at around 11:30am (02:30 GMT), a spokesman at the Japan Coast Guard said.

At least 14 people were killed and some 50 wounded Friday when a gunman opened fire at a crowded cinema premiere of the latest Batman movie in the U.S. state of Colorado, police and media said.

Witnesses interviewed by local media described a scene of chaos at the midnight showing of "The Dark Knight Rises," saying the gunman had set off tear gas bombs and opened fire in the packed theater in Aurora, a suburb of Denver.