Secretary of State John Kerry has called out Iran for what he says is Tehran’s heavy backing of Houthi rebels in Yemen. Speaking to PBS, Kerry said the United States will not tolerate countries that “engage in overt warfare across lines, international boundaries and other countries.”

Secretary of State John Kerry: “We’re very concerned about what’s going on there, and it’s just not a fact. They have been. There are obviously supplies that have been coming from Iran. There are a number of flights every single week that have been flying in, and we trace those flights, and we know this. We’re well aware of the support that Iran has been giving to Yemen. And Iran needs to recognize that the United States is not going to stand by while the region is destabilized or while people engage, you know, in overt warfare across lines, international boundaries and other countries.”

Kerry’s comments come one day after the Pentagon said it would expedite U.S. weapons shipments to aid the Saudi-led military campaign in Yemen.