Stopping short of offering the assurance U.S. senators are seeking, Prime Minister Justin Trudeau said his government is aware there's more work to do in order to see Canada meet NATO's defence spending target.

Responding to a rare bipartisan letter sent by nearly two dozen U.S. senators demanding Canada meet the NATO commitment, the prime minister said: "We recognize there's more to do and we will be there to do it."

"Because we are the ones who are taking seriously Canada's defence needs, and making sure the women and men of our Armed Forces have the right equipment," Trudeau continued, speaking at an event in Nova Scotia.

"Not just to fulfil what their fellow Canadians expect of them, but what our allies around the world are counting on us to do."

On Thursday, as CNN reported, 23 U.S. senators – both Democrat and Republican – wrote to Trudeau imploring him to make good on Canada's commitment to spend two per cent of its GDP on defence. 

Canada has long been painted as a nation not carrying its weight when it comes to supporting the North Atlantic Treaty Organization.

Now, with the 32-member military alliance's 75th anniversary on the horizon, pressure appears to be ramping up again for Canada to step up and join the 18 countries who are on track to meet the spending target by the end of the year.

The senators — including Republicans Mitt Romney and Ted Cruz, as well as Democrats Tim Kaine and Tammy Duckworth — said they decided to write to Canada as it appears to be one of the only laggard nations that's yet to present a plan to reach two per cent.

"As we approach the 2024 NATO Summit in Washington, D.C., we are concerned and profoundly disappointed that Canada's most recent projection indicated that it will not reach its two percent commitment this decade," reads the letter. 

"In 2029, Canada's defence spending is estimated to rise to just 1.7 percent, five years after the agreed upon deadline of 2024 and still below the spending baseline."

Trudeau said Friday that in the conversations he's had with his American colleagues, Canada's investments in upgrading fighter jet capabilities, in NORAD modernization, and Arctic safety have been "extremely well received by the Americans and by allies around the world."

He also made a point of noting that before he came to power in 2015, defence spending under former Conservative prime minister Stephen Harper had dropped to below one per cent for the first time.

"Not only did we start investing in our military, we actually doubled military investments over the past years. We are now on track to reaching over 1.7 per cent of GDP, which is a record high for Canada, and we're not done yet," Trudeau said.

Last month, Canada unveiled an updated defence policy that includes plans to spend $73 billion over 20 years to renew the country's military capacity, but which still falls short of achieving the NATO target.

Concerns have been raised about what it could mean if Canada doesn't meet that spending target, and Donald Trump returns to the White House.

"There is a growing recognition that there's a high risk the next president will be President Trump. And for any senators who see NATO as a very important alliance … they would like to clear away as many excuses as they can, I think, for President Trump to take some significant actions that they think would be detrimental to NATO," former chief of the defence staff Tom Lawson said on CTV News Channel's Power Play on Thursday.

"Like pulling out entirely or more likely declaring a kind of a two-tier NATO where those who don't pay up aren't really going to be protected if attacked."

With files from CTV News' Jeremie Charron