Coordinated pressure by the Obama administration and its European allies has caused a rapid fall in oil revenue to Iran, squeezing that nation’s economy ahead of nuclear talks next month, U.S. officials and industry analysts said Friday.

The financial pain is likely only to increase in the months ahead. On Friday, the White House formally certified that global oil supplies are sufficient to accommodate deeper cuts in Iranian oil imports, a technical step that clears the way for the implementation of even tougher economic sanctions set to take effect three months from now.