Carter spoke at a press conference in London with British Defense Secretary Michael Fallon. It was the first public comment by a US official on the cruise missile failures. The British are part of the coalition striking Islamic State fighters in Iraq, but not doing strikes in Syria.
Russia fired a total of 26 of the long-range missiles at Syrian targets. The officials said it's unclear whether the errant missiles, launched from Russian ships in the Caspian Sea, caused any significant damage in Iran.
The cruise missile attack in Syria was part of an expanding Russian military campaign that began with airstrikes on Sept. 30. US and NATO leaders condemned the attacks as an effort to prop up the Syrian government of Bashar Assad, rather than to target Islamic State fighters.
Russia's use of cruise missiles has also fueled worried about mishaps in the skies over Syria and the need for Moscow to agree to certain flight safety procedures proposed by the US. Carter has made it clear that the US-led coalition will not agree to cooperate with Russia in the fight against the Islamic State and no collaboration is possible as long as Moscow continues to strike other targets.