BEIJING — The Chinese authorities announced on Wednesday the arrests of five suspects described as Islamic jihadists who they say helped orchestrate an audacious attack near Tiananmen Square, the political heart of the nation, that left five people dead.

In a brief message posted on its microblog account, the Beijing Public Security Bureau said the suspects, all ethnic Uighurs from China’s western Xinjiang region, had enlisted a family of three to drive a vehicle across a crowded sidewalk on Monday and then ignite the car at the foot of the Tiananmen Gate. Two tourists were killed and 40 people were injured as the vehicle sped toward the entrance to the Forbidden City. The authorities had previously reported 38 injuries.

The occupants of the car — identified by the police as Usmen Hasan; his wife, Gulkiz Gini; and his mother, Kuwanhan Reyim, names that are identifiably Uighur — died as it went up in flames. The police say that in addition to gasoline and a gas canister, investigators recovered from the vehicle two knives, metal clubs and a banner bearing “religious extremist messages.” The police did not disclose the content of those messages.

“This was a violent terrorist act that was carefully planned and organized,” the statement said.

The police said the five suspects were arrested Monday, 10 hours after the attack, and had confessed their involvement. They said investigators had found long knives and a “jihadist” flag in the temporary residence where the suspects were staying. It is unclear why the authorities delayed the announcement of the arrests by more than a day.