UPDATE 1-Britain's May says will press Trump this week on Bombardier/Boeing row

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OTTAWA, Sept 18 (Reuters) - British Prime Minister Theresa May said on Monday she would press U.S. President Donald Trump this week about a trade challenge by Boeing Co that could endanger thousands of aerospace jobs in Northern Ireland.

May, speaking after talks with Canadian Prime Minister Justin Trudeau, said the two leaders had agreed to work together to oppose Boeing's move against Canadian firm Bombardier Inc , the single largest manufacturing employer in Northern Ireland.

May, who is due to meet Trump on the margins of the United Nations, told a news conference that "I will be impressing on him the significance of Bombardier to the United Kingdom ... I want to see a resolution that protects those jobs in Northern Ireland."

Boeing has accused Bombardier of dumping its new CSeries passenger jet in the U.S. aircraft market, a charge the Canadian firm denies. Bombardier is a major employer in the province of Quebec.

"I am very happy to be working with Prime Minister May to explain to the American administration how Boeing's actions are harmful to workers here in Canada," Trudeau told reporters.

Trudeau reiterated that Canada would not talk to Boeing about a proposed purchase of 18 Super Hornet fighter jets until the firm had dropped its challenge. (Reporting by David Ljunggren; editing by G Crosse)