OTTAWA (Reuters) - The Canadian government determined to return to business as usual on Thursday after a reported convert to Islam shot dead a soldier at the National War Memorial and rampaged through Parliament before being killed himself.

But underscoring tensions in the capital Ottawa, police arrested a man at gunpoint just steps from Canadian Prime Minister Stephen Harper while he and his wife were laying a wreath at the National War Memorial to commemorate the killing of the soldier.

Ottawa Police said the man was arrested for "disturbing the crime scene" at the war memorial. It was not immediately clear what was the man's intent.

"He crossed the tape. We told him not to. He didn't listen,"said a police officer at the scene. The tense moment, captured on camera and seen by throngs of people and politicians who had gathered at the war memorial.

Employees began returning to the Parliament Hill complex amid tighter security. The House of Commons was set to open on schedule.

"This sends a clear message of Canada's resolve to maintain its free and democratic way of life," House Speaker Andrew Scheer said in a statement.

The flag flying over Parliament's Centre Block, where the gunman had burst in on Wednesday morning, was at half mast.

Tighter security was evident all over the sprawling parliamentary zone in downtown Ottawa. Armed Royal Canadian Mounted Police officers stood outside the door where the gunman, identified as Michael Zehaf-Bibeau, rushed in on Wednesday.

Parliament Hill and the downtown core were under lockdown for 10 hours on Wednesday as police scoured the area for more possible suspects.

"There was only one gunman," said a Royal Canadian Mounted Police officer who was guarding Parliament Hill on Thursday morning, checking the identity cards of workers and media going into the parliament complex.

He said in the confusion on Wednesday morning, witnesses saw things from different angles, suggesting the possibility of second shooter but videos and further interviews showed this was not the case.

The killing of the Canadian soldier was the second this week with a possible link to Islamist militants.

In a brief address to the nation on Wednesday night, Harper pledged to redouble the country's fight against terrorist organisations.

"Let there be no misunderstanding, we will not be intimidated. Canada will never be intimidated," he said. "This will lead us to strengthen our resolve and redouble our efforts and those of our national security agencies to take all necessary steps to identify and counter threats."

A convert to Islam on Monday ran over two Canadian soldiers with his car, killing one, near Montreal.

Both attacks took place after Canada announced this month it would send six jets to take part in air strikes against Islamic State fighters who have taken over parts of Iraq and Syria.

Harper said Canada would now "redouble our efforts to work with our allies around the world and fight against the terrorist organizations who brutalize those in other countries with the hope of bringing their savagery to our shores".

Defence Minister Rob Nicholson said Canada's deployment to Iraq would go on unimpeded.

The two attacks in quick succession could push the Canadian government to pause and rethink before introducing a planned bill to change the Canadian Security Intelligence Service Act, said Wesley Wark, a professor at the University of Ottawa, who is an expert on national security and intelligence issues.

The Bill to boost the powers of Canada's main spy agency, CSIS, was slated to be introduced in parliament this week.

"What the government is now confronting is a choice with going forward on whatever its original, probably small-scale changes might have been, or sitting back and thinking about whether there is something more that needs to be done," he said.

Court documents show Zehaf-Bibeau previously faced a robbery charge in Vancouver and multiple drug-related charges in Montreal.

US officials said they had been advised the dead gunman in Wednesday's shootings was also a Canadian convert to Islam.

Treasury Board Minister Tony Clement tweeted that he would convene a regularly scheduled meeting on Thursday and added "#terroristsbedamned".

"The last thing anyone in our community wants is to cower to this outrageous ... murder," Mayor Jim Watson said on CBC radio.