WASHINGTON North Korea is upgrading one of its two major missile launch sites, apparently to handle much bigger rockets, and some design features suggest it is getting help from Iran, a U.S. research institute said Thursday.

A successful satellite launch in December, and a nuclear test on Tuesday, both in defiance of U.N. Security Council resolutions, have intensified concern that North Korea is moving toward its goal of building a bomb small enough to be fitted on an intercontinental missile.

An analysis written for 38 North, the website of the U.S.-Korea Institute at Johns Hopkins School of Advanced International Studies, 홍천출장업소 indicates that North Korea has made significant progress since October in constructing a new launchpad and other facilities at Tonghae, on the country’s northeast coast. The assessment is based on commercial satellite photos, the latest taken in January.

It says design features, including a flame trench covering that protects large rockets from the hot exhaust gases they emit on takeoff, is similar to one at a launch complex in Semnan, Iran, and hasn’t been used by the North before.