A gang of bicycle thieves has been terrorizing cyclists in Riverside Park with fence posts and tree branches for a month, police said. A sketch of one attacker has been made available. View Full Caption NYPD

WASHINGTON HEIGHTS — A gang of bicycle thieves wielding sticks, branches and fence posts has been attacking cyclists in Riverside Park for the past month, police said Thursday.

Four robberies have occurred in Riverside Park between 158th Street and 177th Street since mid-August, police said.

In each instance, the gang pounced on an unsuspecting cyclist late at night, beat him in the head with various blunt instruments, then fled with any valuables they could get, police said.

The first attack occurred after midnight on Monday, Aug. 15 in Riverside Park near 171st Street when a gang of men shoved a 29-year-old cyclist off his Retrospec bicycle then stole the bike, $200 and an iPhone, police said.

The gang next attacked on Aug. 19 at 11 p.m. near West 158th Street when they stole a 32-year-old man’s motorized Schwinn, Motorola cellphone and bicycle chain, according to police.

Then on Aug. 24 at around 11:45 p.m. the thieves tried to rob a 34-year-old man, but he managed to hold onto his motorized bike despite being beaten by a tree branch, police said.

In the most recent incident, a 27-year-old cyclist was attacked by a group of men hiding in the bushes of Riverside Park near West 173rd Street on Sept. 2, at 11:30 p.m., police said.

The gang beat the man with a fence post then stole his motorized Haibike bicycle, backpack, iPhone 6, and water bottle, police said.

Three of the four victims were transported to Columbia Presbyterian Medical Center with injuries that included bruising, swelling, and abrasions to the head. The Schwinn owner refused medical attention for his injuries, police said.

The Haibike owner gave a detailed description of one of his attackers to NYPD sketch artists, police said.

The suspect wears a baseball cap and a stud earring in his left ear and sports a small goatee. There were no descriptions of the other suspects and police did not specify the total number of suspects linked to the crimes.

Anyone with information about this incident is asked to call the NYPD's Crime Stoppers Hotline at 1-800-577-TIPS (8477).