Prime Minister Justin Trudeau called U.S. President Donald Trump on Thursday to ask for an end to U.S. steel tariffs and additional diplomatic assistance in Canada's ongoing dispute with China.

"The two leaders discussed relations with China, including the arbitrary detention of two Canadian citizens in China and Canada's ongoing efforts to secure their release," reads a statement from the Prime Minister's Office.

In December, Canada detained Huawei Technologies chief financial officer Meng Wanzhou at the Vancouver International Airport on an extradition request from the United States. She was later granted bail and is now awaiting court proceedings.

Shortly after Meng's arrest, two Canadian expats living in China — Michael Kovrig and Michael Spavor — were detained. In March, China's Central Political and Legal Affairs Commission accused Kovrig of stealing state secrets passed on to him by Spavor.

According to a source with direct knowledge of the call, Trudeau reminded Trump of the blowback Canada has faced from China since Meng's arrest, placing a special emphasis on the conditions of Kovrig and Spavor's imprisonment.

The pair have had limited access to consular officials and are not allowed to see family or loved ones. They have been confined to single rooms without the ability to turn the lights off in their cells at night.

One month after Kovrig and Spavor were arrested, China sentenced Canadian Robert Lloyd Schellenberg to death in a sudden retrial in January. Schellenberg already had been sentenced to a 15-year jail term for drug smuggling.

Last month, a Chinese court sentenced another Canadian, Fan Wei, to death for participating in a global methamphetamine operation.

The source said that Trump was receptive to Trudeau's request for diplomatic assistance with Canada's efforts to have Kovrig and Spavor freed.

A report from the White House also mentioned the call and Trump's sympathy for Canada's trouble with China.

"During the call, the president expressed the United States' solid commitment to standing by Canada in efforts to secure the fair treatment and release of Canadian citizens currently detained in China," it read.

Trade hurdles

Since Meng's arrest, China also has placed a number of trade hurdles in front of Canadian exporters — banning imports from two canola producers, tying up shipments of pork over paperwork issues, and putting unusual obstacles in the way of Canadian soybean and pea exporters.

The sources said Trudeau also used the call to bring up the difficulties posed by U.S. steel tariffs and to point out that their continued existence could frustrate ratification of the revamped North American Free Trade Agreement.

"The prime minister raised the issue of U.S. steel and aluminum tariffs and reiterated the importance of their removal," the Prime Minister's Office said.

"The prime minister and president also exchanged views on progress toward the ratification of the new North American Free Trade Agreement, and underscored the strength of the mutually beneficial Canada-U.S. economic partnership."

On June 1 of last year, the United States Department of Commerce imposed tariffs of 25 per cent on Canadian steel and 10 per cent on aluminum, citing national security interests.

Canada responded with its own tariffs of 25 per cent on steel and 10 per cent on aluminum, but also slapped a 10 per cent tariff on a long list of consumer items meant to target U.S. politicians in states where those products are made.

That product list included Kentucky bourbon, lawn mowers, ketchup, maple syrup, appliances, boats, and many other items. The federal government said it was targeting goods that Canadians could otherwise buy from domestic suppliers.

Since then, the Liberal government has rolled back some of the retaliatory tariffs, including ones imposed on recreational boats.