US is considering sanctions on countries that do illegal business with North Korea, Secretary of State Rex Tillerson has warned. <br/><br/>He said the White House would soon have to decide whether to impose secondary sanctions on those nations. <br/><br/>The Trump administration has sought to increase pressure on North Korea over its nuclear and missile activities. North Korea is believed to be making progress toward developing a ballistic missile capable of reaching the US.<br/><br/>Tillerson's warning came at a hearing at the US Senate Foreign Relations Committee yesterday. Washington has no trade links with North Korea. <br/><br/>But, has been considering sanctioning companies from third countries who deal with the regime of Kim Jong-un in violation of UN resolutions.