A grenade given as a birthday present has blown up and killed a close aide of the head of Ukraine's armed forces Valery Zaluzhny.

Maj Hennadiy Chastyakov, 39, had returned to his flat with presents from his colleagues and was opening them with his son when the grenade exploded.

Maj Chastyakov was killed and his 13-year-old son left seriously wounded.

Interior Minister Ihor Klymenko said the boy had started turning the ring on the grenade.

"Then, the serviceman took the grenade from the child and pulled the ring, causing a tragic explosion."

Prosecutors clarified later that he had accidentally set off the grenade while trying to take it away from his son.

The blast has been described as a "tragic accident" and the minister appealed to the public to await the outcome of an official investigation. Police said the explosion in the family flat at Chaiky in the western outskirts of Kyiv had been "as a result of careless handling of ammunition".

But it soon emerged that another five grenades had been found in the flat. Mr Klymenko said that they had been a gift from a colleague in the army.

Two similar grenades were later found in a search of the colleague, described as a colonel in the army.

Pictures from the scene showed other grenades on the floor of the flat, along with other gift bags. Maj Chastyakov had apparently brought the grenades home in a bag with a bottle of whisky.

A source told Ukrainska Pravda that the bottle had been in a gift bag with grenade-shaped glasses and the explosion happened when he opened the bag. Other reports said that his colleague had handed over the bottle saying: "It's hard to surprise you: That's why I'm giving you combat grenades and a bottle of good whisky."

Gen Zaluzhny spoke of the unspeakable pain and heavy loss to the Ukrainian military and to him personally, describing Maj Chastyakov as a "reliable shoulder" since the start of Russia's full-scale invasion in February 2022.

His death is the latest setback for the Ukrainian military, after a missile strike killed 19 soldiers in a Russian attack on an awards ceremony close to the front line in the southern region of Zaporizhzhia. There was widespread criticism that the ceremony had been allowed to go ahead in a dangerous area.

Pro-presidential MP Maryana Bezulha said Maj Chastyakov's death was down to negligence: "I would never have thought Hennadiy would die as a result of carelessness on his own birthday. Grenades are issued, not given as presents."

However, the official cause of the explosion has been questioned by Ukrainian commentators, some of whom have speculated whether it was an attack targeting Gen Zaluzhny himself, on the assumption that he might have attended his aide's birthday celebrations.

Last week the commander in chief gave a blunt assessment of the situation on Ukraine's front lines against Russia's invasion forces.

"Just like in World War One, we have reached the level of technology that puts us into a stalemate," he told the Economist. "There will most likely be no deep and beautiful breakthrough."

Both the Kremlin and President President Volodymr Zelensky denied the war had reached deadlock. "Today people are tired, everyone is tired, and there are different opinions. That is clear, but there is no stalemate," Mr Zelensky said at the weekend.

In his regular nightly address on Monday night he appealed to Ukrainians to "pull ourselves together, avoid unwinding and splitting up into disputes or other priorities".

He also announced that "now is not the right time" for presidential elections due to take place next spring, because Ukraine was at war and under martial law. He was elected in 2019.