Greenpeace activists can be seen on the roof of Parliament's West Block building on Dec. 7, 2009. (CBC)

The Mounties say they immediately boosted their presence on Parliament Hill after 19 Greenpeace protesters climbed onto the roof of the West Block in December and unfurled banners calling for action on climate change.

"We have enhanced our presence, significantly enhanced since the event," RCMP Staff Sgt Marc Richer said Thursday.

As to whether Public Works was to blame for the incident, he replied, "You know you don't go around assigning blame."

Work was being done on West Block and in a statement Thursday, a spokesperson for Public Works said all its construction sites are secured according to industry standards.

Since the incident of Dec. 7, Public Works implemented additional security measures, including fencing secured with heavy duty chain and bolted to the ground. The department upgraded interior hoarding and hardware and secured access points to the scaffolding with doors and locks.

The RCMP took more than two months to complete an administrative review of the security breach.

In a news release Thursday, the RCMP said they became aware of the Greenpeace activists only after the protesters were on the roofs of the West Block and Centre Block buildings at about 7:10 a.m. on Dec. 7.

This conflicts with what a House of Commons bus driver told CBC News the morning of the protest. The man said he had noticed a group of people wearing blue overalls, white helmets and climbing gear before they scaled the walls. The driver said he reported what he had seen to the RCMP.

The Mounties said the 19 protesters got into a restricted construction zone by slicing through nylon tie-wraps on a fence before climbing onto scaffolding as a first step in reaching the roofs.

"This group used well-planned tactics to defeat the security systems and the strategies in place on Parliament Hill at that time," an RCMP spokesperson said in an email sent to CBC News on Thursday.

Once they learned of the breach, the Mounties say they took immediate action.

CBC News has learned that only two Mounties were on duty that morning, despite the force having funding for more than 30 officers to look after security on Parliament Hill.

Richer declined to say how many officers were working that morning.

The local Ottawa police force tactical team and fire department removed the climbers, some of whom had rappelled down the side of the buildings. Twenty people were arrested and charged with mischief as well as unlawful assembly.

The Mounties said they have already improved security on Parliament Hill to prevent a similar breach in the future — although for security reasons, they say they can't elaborate on what steps have been taken.