One of the accused gunmen in the infamous Carnegie Deli triple slaying split open a Rikers Island guard's head yesterday in a surprise jailhouse attack, authorities said.
Sean Salley, 30, was placed under beefed-up security after he allegedly ambushed Correction Officer Vincent Donovan about 10 a.m.
Authorities said Salley punched Donovan in the face, causing him to fall backward and slam his head against the bars of a jail cell.
Donovan, 46, was taken to New York Hospital Medical Center of Queens, where doctors closed a 2-inch gash in the back of his head with 10 stitches.
"Sean Salley is one of the most barbaric inmates in corrections," said Norman Seabrook, president of the Correction Officers' Benevolent Association. "I'm extremely upset that an individual like this is not kept in handcuffs and in maximum restraints."
Seabrook described Salley as "an inmate with no respect for the law and with nothing to lose."
Correction Department spokesman Tom Antenen said Salley has been charged with second-degree assault and reclassified as a violent inmate.
Antenen said Salley would now be placed under 23-hour-a-day lockdown and put in enhanced restraints anytime he's outside his cell.
Salley was already being held in Rikers' northern infirmary building, which is reserved for high-profile inmates.
The attack occurred when Donovan opened Salley's jail cell to escort the inmate to his morning shower, officials said.
Earlier, "Salley had some words for the officer" when Donovan conducted a pat search on him, according to a source.
The assault comes two weeks after authorities intercepted a pair of sneakers sent to Salley that contained marijuana hidden in the soles.
Meanwhile, the Carnegie Deli trial continued yesterday in Manhattan Supreme Court without Salley present.
Salley and co-defendant Andre Smith are accused of executing actress-turned-pot dealer Jennifer Stahl, 3, Stephen King, 32, and Charles Helliwell, 36, during a botched robbery in Stahl's apartment above the famed midtown deli. Two other men survived the shooting.
Two juries, one for Salley and the other for Smith, are hearing testimony in the case.
Detective William McNeely testified yesterday that shortly after Smith was arrested, he accused Salley of carrying out all of the shootings when "everything got out of hand."