The RCMP are investigating how 19 Greenpeace protesters in blue jumpsuits and white climbing helmets were able to scale two buildings on Parliament Hill undetected and unveil huge banners from the roof.

It's believed the 14 protesters who climbed to the roof atop the West Block used scaffolding at the back of the building to gain access at about 7:30 a.m. Monday.

The last of them, dangling from ropes at the edge of the steeply pitched roof, were removed by an aerial fire ladder at mid-morning.

But the Royal Canadian Mounted Police, who are responsible for security outside of the Parliament buildings, would not immediately confirm anything.

"Right now it's still under investigation," said spokeswoman Caroline Poulin.

Security on Parliament Hill has been increased in the wake of the terrorist attacks of September 2001. RCMP will no doubt face tough questions about how a group of protesters could easily gain such access to Parliament Hill buildings in the light of day.

Five protesters were escorted off an entrance-way tower to the Senate in the Centre Block about one hour after staking their ground and unfurling a large banner saying "Stop the Oil Sands." Police used a fire truck-mounted ladder to get them down.

But it took more than two hours before police were able to make their way to the West Block roof, where protesters had hung massive banners that targeted both Prime Minister Stephen Harper and Liberal Leader Michael Ignatieff for their climate change policies.

The activists rappelled from a wrought iron fence which rings the roof of the West Block and unfurled banners saying "Harper-Ignatieff: Climate Inaction Costs Lives," in English and French.

Dozens of officers from Ottawa police, Parliament Hill security and the RCMP swarmed the ground beneath the dangling protesters. Fire trucks and ambulance were also on hand, while police fretted about bystanders slipping on the ice. A helicopter and an airplane circled overhead.

Greenpeace said its people did not face any problems climbing the buildings earlier this morning.

When authorities did finally gain access to the roof, their first action was to take down the banners and signs.

The activists have been targeting the oil sands operations in Alberta, but now they want to highlight the government negotiations in Copenhagen this week. There, world leaders are meeting to hash out a new global pact to prevent climate change.

"We thought it was time to bring the message home," said Christy Ferguson, spokesperson for Greenpeace Canada.

The Ottawa protest targets both Prime Minister Stephen Harper and Liberal Leader Michael Ignatieff for their inaction on climate change, said Greenpeace activist Jessica Wilson.

"Climate inaction costs lives," she said, echoing the message.

A recent Greenpeace report concluded that climate change kills 300,000 people every year, and leads to economic losses worth $125-billion (U.S.).