(Reuters) - Belarus, Russia's closest ally, summoned a Polish diplomat to protest what it said was a Polish military helicopter's violation of its border on Friday, but a military official in Warsaw denied any incursion had occurred.
The Belarusian State Border Commission said the Polish Mi-24 military helicopter crossed the border "at an extremely low altitude, flew to a depth of up to 1,200 metres into the territory of Belarus, and then turned back".
Belarus' Foreign Ministry, in a statement quoted by the official BelTA news agency, said it had summoned the Polish charge d'affaires and demanded an investigation.
"Appropriate explanations were demanded from the Polish side and the conduct of a thorough investigation into the incident," the ministry statement said.
In Warsaw, Lieutenant Colonel Jacek Goryszewski, a Polish military operational command spokesman, flatly denied the Belarusian allegation.
"I do not confirm this information. None of the Polish helicopters crossed the border into Belarus. Such a border crossing could not have happened and it did not happen. Our radar systems are unambiguous," Goryszewski said.
Polish Deputy Foreign Minister Pawel Jablonski had earlier called for "great caution" in considering statements by the Belarus military, led by President Alexander Lukashenko since 1994.
"These services are a direct extension of Lukashenko's regime," Jablonski told private broadcaster Polsat.
Poland's longstanding poor relations with Belarus have deteriorated further in recent weeks, and Warsaw, along with the Baltic states of Latvia and Lithuania, has suggested Poland could close its borders if ties worsen further.
Russian President Vladimir Putin in July accused NATO member Poland of harbouring territorial ambitions in Belarus.
(Reporting by Reuters, Alan Charlish, Marek Strzelecki and Ron Popeski; editing by Jonathan Oatis and Cynthia Osterman)