MOSCOW — An attack that never occurred created a brief alarm Wednesday after a news agency erroneously reported that Russian forces had shot down an incoming combat missile that had violated Russian airspace.

The cause of the commotion, which briefly jolted world currency markets, turned out to be a peaceful Norwegian research rocket, fired on a trajectory away from Russia on a previously announced mission to study the polar lights.

But in a sign that some Russian officials remain jittery about the possibility of a nuclear attack from the north, unnamed sources in the Russian Defense Ministry told the Interfax news agency, hours after the report was known to be false, that "it is too soon to tell" if the launch was aimed at testing Russia's early warning radar system.

Norwegian officials were baffled as to how the rocket launch could have been so misconstrued.

"Missiles are going up and going down all the time," said Tore Tanum, a spokesman for the Norwegian Embassy in Washington. "It's a matter of interpreting the radar, I guess."

On Dec. 14, Norway had notified Russia, the United States and other nations that the rocket would be fired from a civilian-run range on the northern island of Andoya, said Capt. Stig Karlsen, spokesman for the Norwegian Defense Ministry.

Karlsen said 607 research rockets have been launched from the same site, although Wednesday's was the largest to date.

"The whole operation was informed about in a normal way, as they do every time they fire a rocket," Karlsen said.

The four-stage, solid-fuel rocket, which weighed six tons and reached a maximum altitude of 900 miles, was designed to study the northern lights during daytime.

While some military experts said it could have been briefly mistaken for a missile, the rocket was launched in the morning, never strayed off course or moved closer than 185 miles from the Russian border and landed as planned in the Spitzbergen archipelago, 969 miles northwest of its launch site, Norwegian officials said.

At 4:15 p.m., the respected Interfax news agency received a call from an unnamed Russian military source announcing that a "combat missile" had violated Russian airspace from a northern European country but that it had been intercepted.

Georgy Viren of Interfax's political information unit said the agency was given false information. But he described the source as well placed, previously reliable and in a position to have access to such facts.