The attack immediately raised the specter of terrorism, with Canada already on alert because of a deadly hit-and-run earlier in the week against two Canadian soldiers by a man who police say was fired up with radical Muslim fervor.

Witnesses said the soldier was gunned down at point-blank range just before 10 a.m. by a man carrying a rifle and dressed all in black, a scarf over his face. They said the gunman then ran off and entered Parliament, a few hundred yards away, where numerous shots soon rang out.

People fled the complex by scrambling down scaffolding erected for renovations, while others took cover inside and barricaded doors with chairs as police with rifles and body armor took up positions outside and cordoned off the normally bustling streets around Parliament.

Police gave no details on how the gunman died. But on Twitter, Member of Parliament Craig Scott credited Parliament sergeant-at-arms Kevin Vickers with shooting the attacker just outside the MPs’ caucus rooms.

“Today is a sad and tragic day for our city and our country,” Ottawa Mayor Jim Watson said. He said it was a tragedy with “origins as yet not fully known, causes not yet fully understood.”

Ottawa police spokesman Chuck Benoit said two or three gunmen were believed to be involved in the attacks.

Gilles Michaud, assistant commissioner of the Royal Canadian Mounted Police, called it a “dynamic, unfolding situation.”

The identity of the slain gunman was not immediately released, and police would not speculate on a motive for the shootings.

Ottawa Hospital said it received two patients, both listed in stable condition, in addition to the soldier.

In Washington, President Barack Obama condemned the shootings as “outrageous,” and in a telephone call with the prime minister, offered U.S. help and reassurance of the American people’s solidarity with Canada.

The U.S. Embassy in Ottawa was locked down as a precaution, and security was tightened at the Tomb of the Unknown Soldier at Arlington National Cemetery just outside Washington.

Tony Zobl said he witnessed the soldier being gunned down from his fourth-floor window directly above the National War Memorial, a 70-foot, arched granite cenotaph, or tomb, with bronze sculptures commemorating World War I.

“I looked out the window and saw a shooter, a man dressed all in black with a kerchief over his nose and mouth and something over his head as well, holding a rifle and shooting an honor guard in front of the cenotaph point-blank, twice,” Zobl told the Canadian Press news agency.

“The honor guard dropped to the ground, and the shooter kind of raised his arms in triumph holding the rifle.”

Zobl said the gunman then ran up the street toward Parliament Hill.

Cabinet minister Tony Clement tweeted that at least 30 shots were heard inside Parliament, where Conservative and Liberal MPs were holding their weekly caucus meetings.

“I’m safe locked in a office awaiting security,” Kyle Seeback, another member of Parliament, tweeted.

The top spokesman for Prime Minister Stephen Harper said Harper was safe and had left Parliament Hill.

“I was just taking off my jacket to go into caucus. I hear this pop, pop, pop. Possibly 10 shots, don’t really know. Thought it was dynamite or construction rather than anything else,” said John McKay, a member of Parliament.

He said security guards then came rushing down the halls, herding them toward the back of the buildings.

“And then we started talking to another woman and she was apparently inside the library of Parliament, saw the fellow, wearing a hoodie, carrying a gun,” McKay said, “and then the implications of this start to sink in.”

Officials canceled two events in Toronto honoring Pakistani teenager and Nobel laureate Malala Yousafzai, including one in which she was supposed to receive honorary Canadian citizenship. She was shot in the head by a Taliban gunman in 2012 for supporting schooling for girls.

The attack came two days after a recent convert to Islam killed one Canadian soldier and injured another with his car before being shot to death by police.

The killer had been on the radar of federal investigators, who feared he had jihadist ambitions and seized his passport when he tried to travel to Turkey.

Canada had raised its domestic terror threat level from low to medium Tuesday because of what it called “an increase in general chatter from radical Islamist organizations.”

In the hours after Wednesday’s attack, police warned people in downtown Ottawa to stay away from windows and rooftops.

Scott Walsh, a construction worker who was in a manhole in front of Parliament Hill, said he heard the shots at the war memorial.

“We’re in construction and we’re used to loud bangs. When people started screaming and running, that’s when I clued, and I saw this guy running” with a gun, he said. “It was intense. I didn’t think it was real. “

He said the gunman had long black hair with a scarf covering the lower half of his face.