KINSHASA (Reuters) - Authorities in Democratic Republic of Congo have expelled a prominent American researcher weeks after he published a report linking soldiers to the massacres of civilians, the government and the researcher’s organization said on Saturday.

Jason Stearns, the director of the Congo Research Group at New York University, was expelled from the country, to which he makes regular research visits, for making false declarations to immigration services, government spokesman Lambert Mende said.

“(Immigration authorities) wanted to present him to a judge but finally they decided to expel him,” Mende said, adding that he did not have any details on the nature of those declarations.

The group said the reason given by authorities for Stearns’ expulsion on Thursday was his “undesirability”, and said the immigration irregularities were “minor procedural matters, which we are taking steps to address”.

Its statement said the authorities referred to Stearns’ report about the massacres, without giving further detail.

Last month’s report said that soldiers in Congo’s army had participated in massacres of civilians in the country’s northeast since 2014, although it said it was unclear to what extent the military hierarchy was involved.

Mende sharply criticized the report at a news conference in the days after it was released, accusing Stearns of “abusive generalization”.

Rights groups say more than 500 people have died in a wave of machete attacks and other raids since October 2014. The government has blamed most of them on a Ugandan Islamist group that has operated in eastern Congo since the 1990s.

Political tensions are high in Congo, where President Joseph Kabila, in power since 2001, is required by the constitution to step down before the end of the year.

Opponents, however, accuse him of trying to delay a presidential election due in for November in order to hold onto power. The United Nations and rights groups say the government is cracking down on dissent through arrests and intimidation of opponents.

The government denies both of these charges.

Stearns is a former coordinator of the U.N. panel of experts in Congo and author of a widely read book about the country’s civil wars from 1996-2003.