North Korea said on Saturday it had detained two Americans for "illegally" entering the country by crossing the border with China. South Korean media and diplomatic sources said this week North Korean security officials detained two female American journalists on Tuesday who were filming across the Tumen River from the Chinese side of the border. "Two Americans were detained on March 17 while illegally intruding into the territory of the DPRK (North Korea) by crossing the DPRK-China border. A competent organ is now investigating the case," the North's official news agency KCNA said without giving more details. A media source has said the two women were working for Current TV, a U.S.-based online news company. A diplomatic source said earlier the reporters were on the frozen Tumen river when taken by North Korean security guards. The Tumen runs along the eastern section of the border with China. The arrests come at a time of mounting tension as the North has said it will launch a satellite early in April as part of its space communication program. U.S. officials say the launch is intended to test a rocket that could potentially carry a warhead as far as U.S. territory.