SEOUL, March 14 (Reuters) - South Korea's foreign minister will visit the United States as planned from Thursday, her ministry said, to maintain "strong cooperation" with Washington regardless of the departure of US Secretary of State Rex Tillerson. "The United States expressed its wish for our foreign minister to visit as planned," said the ministry in text message on Wednesday, noting that minister Kang Kyung-wha would meet Deputy Secretary of State John Sullivan instead. US President Donald Trump fired Tillerson on Tuesday after a series of public rifts over policy on North Korea and other issues, replacing him with loyalist Central Intelligence Agency Director Mike Pompeo.