Writing on his blog where he summarized this week's General Assembly in New York, Bildt said "Prime Minister Netanyahu drew pictures of bombs that left pundits highly confused over what he really meant about Iran and its nuclear programme."
Netanyahu used a red marker diagram of a round bomb with a fizzing fuse, drawing a red line at the top of the bomb and saying the international community must put a limit on Tehran's uranium enrichment.
Bildt said the "trends (in the Middle East) were not positive, and if they're not broken by a different political development then we are headed for something that could be extraordinarily difficult."
He also referenced a speech made by US President Barack Obama two years ago in which he expressed hopes of there being an independent Palestinian state within a year.
"That has, to put it mildly, not happened," wrote Bildt.
Using his official Twitter account, Bildt late on Thursday referenced a meeting with Palestinian Foreign Minister Riad Malki in which the two discussed "possibilities of a peace process with Israel"
"Very difficult situation in the region," wrote Bildt.