Oslo-based solar firm REC Silicon said it plans to close production at a U.S. plant and lay off 400 U.S. workers unless a trade dispute between the United States and China is resolved, sending the company's shares sharply lower. The announcement comes as Chinese President Xi Jinping kicks off an official visit of the United States, beginning in Washington state where the REC plant is located, with differences over trade between the world's two largest economies on the agenda. "The timing of this message is no coincidence, as the Chinese president will arrive in Seattle today," REC Chairman Jens Ulltveit-Moe told Reuters. REC Silicon blamed the unresolved trade dispute between the United States and China over solar products for the layoffs at its Moses Lake plant. It would shut its remaining production capacity if there was no resolution. "We hope to trigger a constructive dialogue that will give us access to the Chinese market," said Ulltveit-Moe.