WARSAW (Reuters) - Poland’s defense minister has accused European Council President Donald Tusk of working with Russia’s Vladimir Putin to harm Polish interests following the 2010 plane crash that killed President Lech Kaczynski and 95 others.

Poland's Defence Minister Antoni Macierewicz speaks during a news conference in Tallinn, Estonia, March 14, 2017. REUTERS/Ints Kalnins

The ministry notified the military department of the National Prosecutor’s Office on Monday that it suspected Tusk, who was Polish prime minister at the time, of an “abuse of trust in foreign relations”.

The move was the latest, and possibly most serious, in an internal political row between Poland’s ruling right-wing Law and Justice (PiS) party and rival Tusk.

Poland was isolated and rebuffed at an European Union summit earlier this month when Tusk, a centrist, was reappointed as council president over Warsaw’s objections.

A spokeswoman for the prosecutor’s office in Warsaw confirmed it had received the ministry’s notification, which effectively accuses Tusk of diplomatic treason. It now has 30 days to decide whether to investigate.

Tusk dismissed the accusations as “purely about emotions and obsessions”.

“This is not a matter of legal or political nature, it is purely about emotions and obsessions,” he said in emailed comments. “Therefore, it is not within my competence to comment on cases like this one.”

The PiS is led by Kaczynski’s twin brother Jaroslaw, Poland’s most powerful politician and a longstanding opponent of Tusk.

Lech Kaczynski died when in a plane carrying a Polish delegation crashed approaching Smolensk Air Base in Russia. He was flying from Warsaw to commemorate the 1940 Katyn massacre of Polish officers by Soviet secret police.

Defence Minister Antoni Macierewicz told the Gazeta Polska Codziennie daily on Tuesday: “Tusk made an illegal contract with Vladimir Putin to the detriment of Poland and should bear criminal responsibility for that.”

State news agency PAP quoted the notification as accusing Tusk of agreeing to terms that prevented Poland from playing a full part in investigating the causes of the crash.

Macierewicz alleged that Tusk failed to secure from the start an agreement with Moscow “to guarantee the participation of representatives of Poland in all investigative activities on the site”, and that this allowed Russia to limit the Polish role.

The notification also accused Tusk of failing to take steps that would enforce the return of the Tu-154 plane wreckage to Poland, the notification said.

Russia has repeatedly refused Poland’s demand to return the Tu-154 wreckage and its black box recorders, citing its own ongoing investigation.

BEYOND NEGLIGENCE

The notification from the defense ministry covers the period from the plane crash on April 10, 2010 to 2014, when Tusk took up his current post as chairman of EU leaders’ summits. The alleged crime carries a sentence of one to 10 years in prison.

“It’s not about negligence, it is about a criminal offense,” Macierewicz said.

Polish prosecutors are already conducting several investigations into the Smolensk crash, including a case against a group of public officials also suspected of acting to Poland’s detriment in the year after the accident.

Tusk has frequently denied any responsibility for the crash, which an earlier official investigation concluded was an accident.

The accusation marks a sharp escalation of the conflict between PiS and Tusk, who led the rival Civic Platform party and was prime minister from 2007 to 2014. PiS has already accused him of neglecting the existence of a fraudulent investment scheme when prime minister and selling off too many Polish businesses to foreigners.

Civic Platform party hopes Tusk may return to Poland after his EU stint and become its candidate for the next presidential election in 2020.