Prime Minister Stephen Harper told his hushed caucus Wednesday morning he felt remorse for surreptitiously ducking into a closet during last week's assault on Parliament Hill, CBC News has learned.

Many Conservative MPs were alarmed at the prime minister's sudden disappearance during the terrifying 15 minutes between the moment Michael Zehaf-Bibeau fired the first shot inside the Parliament buildings and when Sergeant-At-Arms Kevin Vickers entered their barricaded caucus room to tell them the fusillade outside their door had ended with Zehaf-Bibeau's death.

None of those MPs were critical of Harper when reached Wednesday, and all of them said the prime minister didn't owe them an explanation.

"He's the leader of the country, and he was the obvious target," one Conservative MP said. "He didn't need to tell us why he got out of there."

Harper was spirited out of the Parliament buildings moments after Vickers sounded the all-clear while his MPs remained in lockdown for hours until police were assured the gunman was acting alone.

The prime minister has told some MPs he felt terrible leaving them behind while he was hustled off to a more secure location.

Across the Hall of Honour Wednesday, New Democrats were also meeting just as they were one week ago during the attack.

Cheers for 'hero' guard

The NDP MPs applauded Alain Gervais, a House of Commons guard who blocked the door to their caucus room when when the gunshots first rang out.

House of Commons guard Alain Gervais

House of Commons guard Alain Gervais, left, is applauded at the NDP caucus meeting Wednesday. MPs say Gervais used his body to block the door during last Wednesday's gunfight. (Fin Donnelly/Twitter)

MPs from all parties were back in the rooms where they dove under tables and tried to take cover during the shootout that ended in Zehaf-Bibeau's death.

NDP MPs tweeted photos of Gervais with NDP Leader Tom Mulcair and caucus chair Glenn Thibeault from inside the normally private caucus meeting.

​Gervais used his body last week to block the door to the hallway where Zehaf-Bibeau fought a gun battle with security officials. MPs say a bullet hole in the door serves as a reminder of the risk he took. The bullet went through the first set of wood doors and entered a second interior door but stopped there, around the place where Gervais's head was.

Caucus chair Glenn Thibeault recognized Gervais in the large committee room where the party meets and MPs gave him a standing ovation. Gervais was emotional, a caucus source told CBC News. Mulcair shook Gervais's hand and invited him to the podium, where he was applauded again.

Gervais didn't say a lot, but thanked the caucus and said he was very touched by their applause, and that the House of Commons security staff were simply doing their jobs.

"We're here to protect you. That's why we're here," he said.

The New Democrats tweeted their thanks.

"Our hero," Quebec MP Mylène Freeman wrote in French.

"Very grateful for his bravery," tweeted Anne McGrath, the NDP's national director.

Gervais "put himself in harm's way for us," British Columbia MP Fin Donnelly said.

Cross-party solidarity

Before the caucus meetings began, Thibeault and Conservative caucus chair Guy Lauzon met in the rotunda, the grand hall through which Zehaf-Bibeau entered Centre Block last Wednesday, to shake hands in a show of solidarity in front of the cameras.

Caucus chair solidarity1:58

"We got back in the saddle at 10 a.m. the next morning. We've got a strong government, a strong Parliament, and we're going to go forward and keep all Canadians safe and secure," Lauzon told reporters.

"It's an opportunity for all of us to get together … as parliamentarians and to say that we're ready to continue to get back to business, because last week wasn't easy," Thibeault said.

Both men said MPs still feel safe in the parliamentary precinct and expressed their desire to return to focusing on legislation.

The Conservative and NDP caucuses meet in large committee rooms with entrances in the Hall of Honour where last week's shootout happened. At the time, no one knew it was a single gunman: all the MPs knew was that there were dozens of gunshots fired in the hallway next to them.

The Liberals meet in a smaller caucus room one floor below.

Was it 'terrorism'?

After caucus, reporters discovered some disagreement between NDP Leader Tom Mulcair and Liberal Leader Justin Trudeau over how to describe what happened last week.

Mulcair said he wouldn't call the shooting terrorism, the way Prime Minister Stephen Harper did last Wednesday and U.S. Secretary of State John Kerry did on Tuesday.

Mulcair: Don't call it "terrorism"1:31

"I don't think we have enough evidence to use that word," he said. "When you look at the history of the individual involved you see a criminal act, of course. You see something that was meant to provoke the type of reaction that we had," he said.

"But when you look at the history of the individual, attempts to get help, even to be in prison to get help if that turns out to be the case, I think that we're not in the presence of a terrorist act in the sense that we would understand it. And I think that we have to be very careful about the use of the word terrorism, and make sure that that's actually what we're dealing with."

"Frankly the information that is now available to the public comforts me in my choice not to use the word terrorism in describing the act," he said. "That's our point of view. That's my point of view." 

During question period, Mulcair again pointed to what he described as "the fundamental difference between the horrific acts of a profoundly disturbed individual, and organized terror," and urged the Conservatives to work with the other parties "to decide together the best legislative reaction to these horrific events."

In response, Prime Minister Stephen Harper said there was "no contradiction in individuals who may have a series of personal financial and mental difficulties, and also be engaged in terrorist Jihadist activities." 

"We do not think it helps Canadians to do anything but address these matters head on, face them for what they are, and this government will take its responsibilities seriously and bring forward measures to protect the country," he added. 

Trudeau, on the other hand, was not reluctant to use the word.

Trudeau: RCMP calls it "terrorism"5:10

"The RCMP was clear: these were acts of terrorism," he said, adding that the measures put forward to ensure the safety of Canadians would be something that they would "take very seriously." He said the Liberals would look at proposed legislation to see whether it will improve the safety of Canadians and "protect our values and our identity."

Conservative MPs did not hesitate to call last week's violence terrorism.

with files from Catherine Cullen, Laura Payton, Rosemary Barton and Janyce McGregor