"We have listened carefully to the explanation of the NATO effort to help with the refugee flows, we welcome it if it's primarily focused on saving lives," Lacy Swing said.
"On the other hand, we have to be very prudent and careful that the operation doesn't put migrants' lives in danger when they go after the smugglers. The other concern would be that this is part of a much larger and comprehensive policy, because stopping the smugglers is only one element in a comprehensive migration strategy," he added.
Currently, the European countries are struggling to find a solution to a massive migrant crisis, with hundreds of thousands of people leaving conflict-torn countries in the Middle East and North Africa for Europe. Over 1.83 million illegal border crossings were detected by the EU border agency Frontex in 2015.
NATO Secretary General Jens Stoltenberg announced on Thursday plans to deploy warships in the Aegean to combat migrant trafficking into Europe. Its maritime group would be tasked with reconnaissance, monitoring and surveillance of illegal crossings from Turkey, Stoltenberg said.
On Friday, he added that the military bloc would step up monitoring and surveillance along the Turkish-Syrian border to assist Ankara in managing the refugee crisis.