Other towns along the 90-mile-long Serb-held territory, known as Krajina, were also reportedly shelled or bombed.
The Secretary General writes that there never was an enforcement concept behind the "safe areas" - six towns surrounded by Serb-held territory.
The trains took them to Doboj, a city deep in Serb-held territory.
It is not clear how many of the harrassed people have actually left for Serb-held territory.
Some 750 monitors - about 55 of them Americans - are based on Serb-held territory.
He said at least one of the shells had landed in Serb-held territory.
The report said the order was necessary to feed and house the population on the Serb-held territory.
A Bosnian victory closing the corridor would probably doom all Serb-held territories to the west.
Sturlic is 18 miles north of Bihac town, close to the border with Serb-held territory in Croatia.
Safety lay a three-day trek away, through Serb-held territory.