NEW YORK/MONROVIA (Reuters) - Four survivors of a church massacre that killed 600 people during the Liberian civil war on Monday filed a civil lawsuit in U.S. court against the man they accuse of having ordered the attack.

The lawsuit, brought in federal court in Philadelphia, accuses Moses Thomas of directing the mass killing on July 29, 1990, while a colonel in the Armed Forces of Liberia. Thomas came to the United States under an immigration program intended to help victims of the conflict and now lives in a Philadelphia suburb, according to the lawsuit.

Attempts to reach Thomas were unsuccessful late on Monday, but he told the BBC that the allegations were “nonsense,” according to a report on the broadcaster’s website.

The church killing was among the most brutal atrocities committed against civilians during 14 years of near-constant conflict, which saw child soldiers enlisted in the war before it ended in 2003.

Hundreds of families took refuge at St. Peter’s Lutheran Church, a Red Cross humanitarian shelter, in the country’s capital of Monrovia, seeking protection from the violence ravaging the city.

Thomas headed up the army’s elite anti-terrorism unit, according to the lawsuit, and ordered approximately 45 soldiers to enter the church and open fire indiscriminately. Soldiers then used machetes to hack others to death, while some victims survived by hiding under the bodies of others.

The lawsuit can only recover monetary damages from Thomas if successful. It could potentially lead to other actions against him, but lawyers for the victims noted that Liberia has never established a tribunal to investigate wartime human rights violations.

The case was filed under U.S. laws that allow foreign victims of war crimes abroad to sue the perpetrators in U.S. courts.

“Cases like these should be tried in the countries where the crimes were committed,” Nushin Sarkarati, an attorney with the Center for Justice and Accountability, which represents the four anonymous plaintiffs, said in a statement. “Because that is not yet possible in Liberia, the victims have to push to try perpetrators in the courts of the countries where they have chosen to hide.”

Activists hailed the case as a first step toward holding those responsible for the church massacre accountable.

“I think victims and survivors of the St. Peter Lutheran Church massacre will be at peace this evening,” said Peterson Sonyah, executive director of the Liberia Massacre Survivors Association.