The Syrian rebel groups communicated plans for a "major offensive" to Turkey six months ago, two sources familiar with the matter told Reuters.
According to the report, the groups felt they had received "tacit approval" from Turkey following the communication.
The sources, a diplomat in the region and a member of Syria's opposition, said that there was "no way" the rebels could move forward without informing Turkey of their plans.
Turkey has been a supporter of the opposition since the war's early days, and has troops deployed in northwestern Syria. However, the country has opposed a rebel attack due to fears of a large influx of refugees.
According to the opposition source, the rebels' message to Turkey was, "You don't have to do anything, just don't intervene."
Nuh Yilmaz, Turkey's deputy minister for foreign affairs, told a conference on Saturday that Turkey was not behind the offensive and was concerned about instability in the region. It was not precisely correct to say that the rebels' attack was carried out with Turkish approval, sources said.
Speaking on condition of anonymity, a US official told Reuters that the US was aware of Turkey's general support for the rebel groups but was unaware of any tacit approval for a rebel attack.
The Reuters report also noted that the Hezbollah terror group had withdrawn much of its force from Syria due to a need for reinforcements in Lebanon.