Turkish President Recep Tayyip Erdogan on Tuesday doubled down on his warning that Turkey could “come all of a sudden one night” in response to perceived Greek threats, suggesting a Turkish attack on its neighbor cannot be ruled out.

Questioned about his earlier use of the phrase and the possibility of Turkish military action against its NATO ally, Erdogan reiterated the expression.

“What I’m talking about is not a dream,” he said at a news conference in the Bosnian capital Sarajevo. “If what I said was that we could come one night all of a sudden [it means] that, when the time comes, we can come suddenly one night.”

Turkey and Greece have decades-old disputes over an array of issues, including territorial claims in the Aegean Sea and disagreements over the airspace there. The friction has brought them to the brink of war three times in the last half-century.

Ankara says Greece is violating international agreements by militarizing islands close to Turkey’s Aegean coastline. It has also accused Greek air defenses of locking on to Turkish fighter jets during NATO exercises over the eastern Mediterranean.

Athens has also accused Turkey of violating its airspace.

“There are some illegitimate threats against us and if these illegitimate threats continue there’s an end to one’s patience,” Erdogan added, sitting alongside Bosnia’s three presidential representatives.

“When the time is due, necessary action will be taken because it is not a good sign to lock on radars to our planes. Such things done by Greece are not a good sign.”

Erdogan has previously said Turkish forces can “come all of a sudden one night” when threatening military action against Kurdish militants in Syria and Iraq. Turkey has conducted several military operations against the militants in recent years.

He first used the phrase in connection to Greece at an aerial technology festival on Saturday.