Canadian Prime Minister Justin Trudeau has said he will attend the North Atlantic Treaty Organization (NATO) Summit on July 11-12 to discuss trans-Atlantic security issues and challenges with other NATO leaders. "NATO is a cornerstone of Canada's international security policy, and an important alliance as we look for more stability in a world going through rapid change. I look forward to meeting with leaders from NATO member states in Belgium to deepen our already strong relationships, and to discuss what more we can and must do to advance peace and security for our citizens and people around the world," Trudeau said on Monday, Xinhua reported. The summit comes amid escalating tensions between Trudeau and US President Donald Trump. Weeks before the summit, Trump sent Trudeau a letter calling on Canada to increase its defence spending on NATO. The Canadian Press reported that Trump's letter expressed "growing frustration" in the US over what Trump perceives to be a lack of defence spending by NATO allies. Trump has publicly attacked NATO allies for not increasing their spending. Early June, he has berated Trudeau in an ongoing trade spat after slapping tariffs on Canadian steel and aluminium. Over the weekend, Trump also threatened "reciprocity" against trade partners who have imposed or are planning to impose retaliatory tariffs on US goods. NATO, also called the North Atlantic Alliance, is an intergovernmental military alliance of 29 North American and European countries. The alliance is based on the North Atlantic Treaty that was signed on April 4, 1949. It constitutes a system of collective defence whereby its independent member states agree to mutual defence in response to an attack by any external party, with its headquarters located in Brussels.