Renewed conflict on the Korean Peninsula could kill hundreds of thousands of people in the first few days alone even if no nuclear weapons are involved, according to a new report by the U.S. Congressional Research Service.

Given population densities on the peninsula, military conflict "could affect upwards of 25 million people on either side of the border, including at least 100,000 U.S. citizens," according to a 62-page assessment sent to U.S. lawmakers Friday and obtained by Bloomberg News.

The grim report comes after tensions between the U.S. and North Korea peaked over accelerated missile and nuclear weapons tests by Kim Jong Un's regime, exacerbated by a war of words between Kim and U.S. President Donald Trump.