WARSAW (Reuters) - Poland’s Lech Walesa, who shot to world fame for his role in the collapse of communism, promised on Thursday to defend himself in court against new allegations that he collaborated with the communist-era secret services.

Slideshow ( 5 images )

The state history institute said it had confirmed as genuine some documents offered to it by the widow of a communist interior minister suggesting Walesa, ex-leader of the Solidarity union movement that brought down communism in Poland, had been an informant of the communist regime in the 1970s.

“The personal file contains an envelope and in it there is a manually written commitment to collaborate with the secret service signed: Lech Walesa “Bolek”,” said a spokesman for the institute.

Walesa, 72, immediately issued a statement saying he signed no such commitment and suggested it was forged. “I will prove it in court,” he wrote in a blog.

Deputy Prime Minister Mateusz Morawiecki said earlier this week “Walesa has an agent’s past, of course he does. For the last 27 years I not only suspected this but was almost sure”.

Walesa years ago acknowledged signing a commitment to be an informant for Communist Poland’s security organs but insisted he never did anything to carry it out. A special court exonerated him in 2000, saying it found no proof of collaboration.

The Institute of National Remembrance is close to the ruling Law and Justice party (PiS) and the new allegations against Walesa surfaced two months after he accused the conservative nationalist party of acting to undermine Polish democracy since winning an election majority in October.

PiS leader Jaroslaw Kaczynski is a former senior Solidarity official but he and Walesa have long been at loggerheads.

Their conflict dates to 1990 when Walesa, soon after being elected president, dismissed Jaroslaw and his late twin brother, Lech, from positions in his office. Jaroslaw Kaczynski has since maintained that Walesa was once a communist collaborator.

Tensions rose in December when Walesa, who won the Nobel Peace Prize for his Solidarity leadership and retains influence on public opinion in Poland, called for early elections to head off what he said was a threat to democracy posed by PiS policy.

Poland overthrew communism in 1989. Walesa served as president from 1990 to 1995 and Poland joined the EU in 2004.

Last month, the EU began an unprecedented inquiry into whether the PiS government has breached EU rule-of-law standards by passing laws that critics said rein in the constitutional court and public media. On Feb. 4, legislation was passed to heighten the government’s surveillance powers.