Montreal Mayor Denis Coderre didn't hold back during a joint news conference with Liberal Leader Justin Trudeau on Thursday, promising to ensure proposed drug-injection sites open in the city — even over federal objections.

The mayor, who met Trudeau to discuss issues including safe injection sites, has previously said he would give the federal government until the end of the summer to approve four locations in Montreal.

Coderre made it clear he will move ahead regardless.

"I will do it anyway," Coderre said.

Pressed for specifics on timing, the mayor said to stay tuned.

"It is coming; check the memo, you'll receive it," he said.

A question of public safety, Coderre says

The Supreme Court, Coderre said, has been clear on the effectiveness of safe injection sites.

In a 2011 ruling, the high court ruled Vancouver's Insite location saved lives and improved health without leading to higher drug use or crime in the surrounding area.

Heroin Overdoses 20141014

An injection kit is shown at Insite, a safe injection facility in Vancouver. (Jonathan Hayward/Canadian Press)

The court said the government should "generally grant an exemption" required to operate a supervised injection site legally if evidence indicates the site will cut the risk of death and disease, and have little impact on public safety.

The Conservative government proceeded to pass the Respect for Communities Act, which sets out 26 criteria for reviewing an application.

Several health groups, including the Canadian Nurses Association, believe the new law is designed to block the creation of the injection sites.

"It's about public safety," Coderre said. "It is about public health. And all we are asking is to be consistent with what the
Supreme Court has said."

Trudeau praised Coderre's approach.

"Denis has an obligation to the citizens of Montreal to bring forward solutions to make people's lives better, to keep them safe, and I applaud him for moving forward on this," Trudeau said.

"I look forward to supporting him once we form the next government."

Cactus Montreal is a community group that is expected to operate the city's first safe injection site. 

Louis Letellier de St-Just, who chairs the board of directors, said the mayor is doing "what he should do."

"He is pushing this dossier forward," he said. "But the financing has to come from somewhere, and it's not the city who will take it on — it's the Quebec government which will finance it."

Province backs Montreal proposal

The Quebec government has approved Montreal's proposal but it is unclear if money will flow if the feds do not provide the legal green light.

Stephen Harper's Conservatives are adamantly opposed to the sites.

Health Minister Rona Ambrose has used the issue to take aim at Trudeau for pledging to open "drug-injection houses."

Her spokesman, Michael Bolkenius, said in a statement Thursday that such places "allow the use of dangerous and addictive drugs that tear families apart.

"We oppose, and are deeply concerned with, the Liberal leader's pledge to blindly open drug-injection houses in communities across Canada," Bolkenius said.

Coderre said he has a meeting scheduled for Friday with Green party Leader Elizabeth May to discuss the issue, as he is trying to reach out to all political leaders.