LAS VEGAS  — A Greek- American police officer was on life support Tuesday after being shot during a protest on the Las Vegas Strip, the latest in a handful of attacks on police amid demonstrations across the country over the killing of George Floyd in Minneapolis.

29-year-old officer Shay Kellin Mikalonis, member of St John's Greek Orthodox church in Las Vegas, was shot as police tried to disperse a large crowd of protesters in front of a casino shuttered because of the coronavirus. 

At about the same time and less than three miles (4.8 kilometers) away, police outside a federal courthouse shot a protester who was wearing a black tactical vest and armed with two handguns and a rifle. Police said the man was shot as he reached for a firearm. 

In other violence around the country, four officers were shot and wounded in Missouri and others in New York were hurt when a car plowed into a line of police.

"With these protests, which are leading to riots, one tragedy is only leading to another," said Clark County Sheriff Joe Lombardo, who heads the Las Vegas Metropolitan Police Department. 

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The incidents came amid chaotic scenes that followed peaceful protests over the killing of Floyd, police brutality and racism. A number of cities have seen heavy-handed riot tactics by police and clashes between officers and demonstrators..

On Monday night, as protests started to dwindle in St. Louis, four officers standing in a line were shot and injured when someone opened fire. All four were expected to recover. In the same city several hours later, police said four officers in a marked police car were fired on by men in a car. 

Police in Buffalo, New York, said an SUV broke through a police blockade at a protest and ran over a state trooper, breaking his leg and shattering his pelvis. Another trooper and a Buffalo police officer were also hit by the vehicle and treated for minor injuries.

In Madison, Wisconsin, police Chief Vic Wahl said police officers were struck with rocks and projectiles.

Over the weekend, police in Los Angeles reported rocks and other objects rained down on police at a demonstration near an outdoor mall, leaving one officer with a fractured skull. In Oakland, California, violence Friday night left 13 officers injured and a federal officer was fatally shot from an unidentified vehicle while providing security at a courthouse during a protest. Dave Patrick Underwood, 53, died and another officer was critically wounded, authorities said. 

Lombardo said officers in Las Vegas were being hit by rocks and bottles when a shot rang out and the officer, Shay Kellin Mikalonis, went down on the casino-lined Las Vegas Strip. 

Police said Mikalonis, a Las Vegas police officer for four years, was shot from across the street and 20-year-old Edgar Samaniego of Las Vegas was identified by video before he was later arrested on suspicion of the shooting.

Jail and court records showed Samaniego was being held pending an initial court appearance on attempted murder and weapon charges. An attorney who represented Samaniego in a personal injury lawsuit in 2016 declined to comment, saying he was not immediately representing him on the criminal charges.

Deputy Police Chief Chris Jones told reporters the man killed by police near the courthouse, 25-year-old Jorge Gomez of Las Vegas, had one of his three handguns mounted in what Jones called a "carbine conversion kit" that officials say made it resemble a rifle.

Gomez remained near the courthouse after police ordered what the deputy chief called "rowdy" demonstrators to disperse, and was hit several times with beanbag projectiles before he was shot as he raised a gun toward officers who were helping an officer on the ground, Jones said.

 Lombardo and local officials pleaded multiple times in recent days for events to remain peaceful. They have so far resisted calls to impose a curfew in Las Vegas. 

Nevada Gov. Steve Sisolak said Tuesday he was praying for the "officer who was senselessly shot" and "all of the communities across Nevada who are experiencing grief and pain."

"It's during these trying times we must remind ourselves that creating a state where justice and peace exist together in partnership, not as a binary choice, is the goal we must all work toward," he said.

Sisolak said he was activating "additional" members of the Nevada National Guard to support state and local law enforcement at the protests. He initially deployed the Guard over the weekend. The governor's office said the Guard units would not be making arrests or doing crowd control but would "focus on protecting critical facilities, preserving public safety, and allowing individuals to exercise their rights to peacefully demonstrate."

Monday's protest began near President Donald Trump's non-casino hotel, Trump International Tower, just off the Las Vegas Strip and remained peaceful for more than four hours.

"All night long, everybody worked hard to keep everybody safe," said U.S. Marshal Gary Schofield, head of the local federal security agency involved with police in the shooting in front of the courthouse. "Unfortunately, criminals hijacked the event."