4:20 a.m. International Space Station crew moves away from Ammonia Leak (Jan. 14, 2015)

A problem in the U.S. segment of the International Space Station on Wednesday prompted its six-person crew to quickly lock it up and move to a Russian module, but they aren't in danger, Russian and U.S. officials said.
"The space station crew is safe," NASA spokesman Bob Jacobs said.
According to a NASA official, a "very small" ammonia leak was detected around 4:20 a.m. EST, CBS News space consultant William Harwood reports. The crew donned masks as a routine protective measure, moved into the Russian section of the space station and closed hatches to isolate the U.S. section.
Russia's space agency Roscosmos said in a statement that a "leak of harmful substances from the cooling system" prompted the crew to isolate the American module.
"The crew is safe and is in the Russian segment now," it said in a statement, adding that mission control experts in Moscow and Houston quickly and efficiently cooperated to ensure the crew's safety.
While Roscosmos said there was a leak, NASA said in a statement broadcast on its online television station there was still "no concrete data that suggests that there was in fact an ammonia leak."
"We saw an increase in water loop pressure, then later saw a cabin-pressure increase that could be indicative of an ammonia leak in the worst case scenario, so we protected for the worst case scenario and isolated the crew is the Russian segment of the space station while the teams are evaluating the situation," Jacobs said.
www.cbsnews.com/ with updated information 9 a.m. Eastern Time.