A US Navy Boeing P-8A Poseidon patrol plane has left Varna and flown to Sigonella air base in Sicily. Before that, it was watching the western Black Sea, data from a military flight-tracking site shows.

There is no official confirmation that its mission from Bulgarian territory has ended.

How it all started: Radev: US plane is already scouting for risks over the Black Sea

The plane landed in Varna on 18 October, reportedly arriving from Sigonella. On 20 October, prime minister Rumen Radev said in Tvarditsa that the aircraft was already flying reconnaissance missions over the sea, and that this was the result of his talks with NATO and Bulgaria's partners. He said the plane looks for possible threats. The flights are part of heightened vigilance after Bulgaria asked its NATO allies for support.

The P-8A Poseidon is a US Navy aircraft for maritime patrol and reconnaissance. It has systems to detect and track surface vessels and to detect submarines. Flight data shows it flew long patterns over the sea, east of the Bulgarian coast.

The missions began as tension in the region grew and merchant ships in the Black Sea came under attack. In early October, drones hit several ships near Bulgaria and Romania, raising fears for the safety of international shipping.

How long the plane stays depends on the situation, Radev said on 20 October.