U.S. Defense Secretary Robert Gates wants to see the United Nations slap sanctions on Iran in "weeks, not months."

Pentagon spokesman Geoff Morrell told reporters Tuesday that Gates "clearly thinks time is of the essence."

Gates is returning to Washington after spending a week in Europe. In Paris on Monday he met with French President Nicolas Sarkozy. Gates also met with NATO officials in Istanbul to discuss Afghanistan, including ways to address a shortfall of 4,000 military trainers.

Morrell says Gates believes a U.N. resolution would lay the legal groundwork countries need to impose sanctions independently and pressure Iran to abandon its nuclear program.