Britain is pressing for US plane maker Boeing to drop its trade challenge against Canadian rival Bombardier and seek a negotiated settlement to try to protect jobs in Northern Ireland.

UK Prime Minister Theresa May also raised the issue in a call earlier this month to US President Donald Trump, after Boeing complained earlier this year that Bombardier was dumping passenger jets on the US market. 

Bombardier is Northern Ireland's largest manufacturing employer. 

"Ministers across government have engaged swiftly and extensively with Boeing, Bombardier, the US and Canadian governments. Our priority is to encourage Boeing to drop its case and seek a negotiated settlement with Bombardier," a UK government spokesman said in a statement. 

"This is a commercial matter but the UK government is working tirelessly to safeguard Bombardier's operations and its highly skilled workers in Belfast," the spokesman added.

In April, Boeing asked the Commerce Department to investigate alleged subsidies and unfair pricing for Bombardier's CSeries airplane.

Boeing accused the Canadian company of having sold 75 of the planes to Delta Air Lines last year at a price well below cost. 

The allegations were denied by Bombardier and the challenge has strained ties with Canada. 

"Boeing had to take action as subsidised competition has hurt us now and will continue to hurt us for years to come, and we could not stand by given this clear case of illegal dumping," Boeing said in a statement.

"We believe that global trade only works if everyone plays by the same rules of the road, and that’s a principle that ultimately creates the greatest value for Canada, the United Kingdom, the United States, and our aerospace industry," the company added.