Secretary of State John Kerry has said that the United States knew Iran had been providing military support to the Houthi rebels in Yemen and that Washington “is not going to stand by while the region is destabilized.”

Mr. Kerry’s remarks, in an interview on Wednesday night with “PBS NewsHour,” appeared to be the most direct warning yet from Washington about Iranian support for the Houthi movement, which has allied with security forces loyal to a former leader and has taken control of Yemen’s capital, Sana.

The comments come as the United States has increased its provision of weapons, intelligence and logistical support for a Saudi-led campaign of airstrikes aimed at preventing the Houthis and their allies from dominating Yemen. […]