WARSAW (Reuters) -Two top Polish army commanders resigned on Tuesday, spokespeople said, days before an election in which the ruling Law and Justice (PiS) party has made national security a key issue in its bid for an unprecedented third term in power.

They come against a backdrop of heightened tension between the military high command and the nationalist government since Defence Minister Mariusz Blaszczak in May said the army had failed to inform him of a missile heading toward the country.

Polish media reported that a military object found in a forest in northern Poland in April was a Russian KH-55 missile, and that Polish armed forces had seen an object entering the country's air space in December but then had lost track of it.

The armed forces operational commander, Lieutenant General Tomasz Piotrowski, and the chief of staff, General Rajmund Andrzejczak, submitted their resignations on Tuesday, spokespeople for the respective services confirmed to Reuters.

No reason was given for the departures.

President Andrzej Duda appointed Lieutenant General Wieslaw Kukula as chief of staff and Major General Maciej Klisz as armed forces operational commander.

The resignations were first reported by Rzeczpospolita daily. The defence ministry declined to comment.

"(It is) a complete disgrace for Minister Blaszczak, who has long crossed over the line into using the Polish army in a partisan way," Tomasz Siemoniak, a former defence minister from the opposition Civic Platform, wrote on social media platform X, formerly known as Twitter.

"This is a PiS disaster in the defence sector at a time of great threats to Poland," he said.

Civic Platform head Donald Tusk, a liberal and former prime minister, said he received information that another 10 senior officers had handed in their resignations on Tuesday.

A spokesperson for the general command confirmed that 10 other officers had quit but "they were not high ranking" and their departures were not unusual. "People retire and just hand in their notice," the spokesperson said.

Rattled by Russia's invasion of neighbouring Ukraine, Poland has increased military spending to around 4% of national output this year and has also moved soldiers to its border with Belarus, a close ally of Moscow.

With a closely contested election in Poland on Oct. 15, experts said the pace of military spending and the domestic debate around it were being driven in part by campaigning.

(Reporting by Karol Badohal, Pawel Florkiewicz, Anna Wlodarczak-Semczuk and Alan Charlish; Editing by Gareth Jones, Mark Heinrich and Mark Porter)