Serbia's Defence Ministry has denied they were involved in the fatal crash of a Bulgarian MIG-29 fighter jet earlier in June.
The aircraft lost contact with Bulgaria on June 9 and disappeared while conducting a military training mission at sea off the country's east coast.
On Thursday, Bulgarian Defence Minister Georgi Panayotov confirmed that authorities had also recovered the plane's "black box" and hoped it could provide information on how the plane crashed.
Some Bulgarian journalists had claimed that Serbian military planes had shot down the MIG-29.
But in a statement, Serbia's Defence Ministry described the allegations as "inaccurate and malicious".
"Members of the Serbian Air Force and Air Defence did not act on air defence missile units on the day of the Bulgarian MiG-29 crash," the ministry said.
"Nor can the actions of our aviation at the Shabla range be connected in any way with the crash."
The Ministry said the country's military had always followed agreements with Bulgaria when carrying out military exercises in the area. Bulgaria has also denounced any speculation about how the MIG-29 crashed.
"I urge all speculation in the media to stop, they are unnecessary," said Panayotov on Thursday.
"We are talking about the memory of a Bulgarian hero. Let the responsible authorities do their job," he added.
Bulgaria said the aircraft had taken off from Graf Ignatievo Air Base and had been performing a military exercise before contact was lost on June 9 at 00:45 (23:45 CEST June 8).
"The pilot was in the area of Shabla was performing a task at night on a luminous target launched by another plane," the ministry has said.
"The target fell at a higher speed, which required an additional maneuver ... the pilot hit the target, reported that he hit it, and shortly after that, the connection with him was terminated."
A search and rescue operation was immediately launched to find the jet and its pilot, Major Valentin Terziev. One day after the plane's disappearance, Bulgaria's Defence Ministry confirmed that Terziev had been killed in the incident.
The wreckage of the plane, including parts of the engine and landing gear, was not discovered in the Black Sea until June 17.
"Major Valentin Terziev is a first-class pilot with extensive experience in flying, including at night," added Panayotov.
The Minister also thanked the Bulgarian Navy on Thursday for recovering the plane's black box to assist with the investigation.
"The plan to find and retrieve the black box was meticulously and perfectly executed," he said, "the Navy literally found a needle in a haystack."
Bulgaria currently has 16 MiG-29 fighters, of which only six are operational, to monitor its airspace.