BEIRUT, Lebanon — Relatives of Marie Colvin, a veteran American war reporter who died more than four years ago in an artillery barrage in Syria, have filed a wrongful-death lawsuit against the Syrian government, accusing it of targeting and killing her as part of a systematic strategy to silence civilian journalists and activists covering the war.

The civil complaint, filed Saturday in federal court in Washington, contends that high-ranking Syrian officials, including President Bashar al-Assad’s brother Maher and other top advisers, worked in concert to locate, track and target foreign journalists and Syrians who had helped them. It lays out new details of the events leading to Ms. Colvin’s death, citing witnesses and government sources and documents uncovered in what the family’s lawyers described as a three-year investigation.

Ms. Colvin, a longtime correspondent for The Sunday Times of London, was killed on Feb. 22, 2012, along with a French photojournalist, Rémi Ochlik, when Syrian government forces shelled an apartment building used by journalists.

The attack occurred during weeks of bombardment of the rebellious neighborhood of Baba Amr in the city of Homs — the first of many operations in which government forces used siege tactics and indiscriminate shelling against rebel-held areas — and before the emergence of extremist Islamist militant groups like the Nusra Front and the Islamic State.