By Agence France-Presse Washington's top trade negotiator said Tuesday he is working with Canadian and Mexican officials to find a compromise on US steel and aluminum tariffs. US Trade Representative Robert Lighthizer said quotas on steel and aluminum imports might be an alternative to tariffs for Mexico and Canada (AFP Photo/Jim WATSON) President Donald Trump imposed the tariffs worldwide last June, citing national security grounds to protect US industry, and they continue to hit Mexican and Canadian producers even after the three countries in November signed an updated free trade agreement. Officials in Ottawa and Mexico City say the metals tariffs are an obstacle to ratifying the new United States-Mexico-Canada Agreement. "We're in discussions with them and trying to find a way out of that dilemma for them and for us," US Trade Representative Robert Lighthizer said in testimony before a Senate committee. He said Washington wanted to ease the tariff burden on its North American trading partners, which together are the largest source for imports of the metals, without losing the protections the duties provide to US companies. "The question becomes how do you relieve the burden of the tariffs on steel and aluminum on Canada and Mexico and still maintain the integrity of the program," Lighthizer said. Quotas are an option, but they would have to be imposed in a way that ensures Mexico and Canada do not "take advantage" of the limits, effectively using the US tariffs' to their advantage. "All I'm saying is I think there's a sweet spot there. Quotas are not necessarily good or bad. It depends on the level of the quota," he said. "It's something that we're working on very hard at this point."