United Nations Secretary General Ban Ki-moon said on Thursday that he is “gravely concerned” about the news that the most prominent opposition activist in Myanmar – Aung San Suu Kyi – has been imprisoned in the country's notorious Insein prison to face charges stemming from a reportedly “uninvited” visit by a U.S. activist. “The secretary general believes that Daw Aung San Suu Kyi is an essential partner for dialogue in Myanmar's national reconciliation and calls on the government not to take any further action that could undermine this important process,” said a statement from Ban's press office. Daw is an honorific equivalent to ‘madam.' “As he has said repeatedly, the secretary general believes strongly that Daw Aung San Suu Kyi and all those who have a contribution to make to the future of their country must be free to be able to do so to ensure that the political process is credible,” the statement added. Reports say Suu Kyi was charged under the country's Law Safeguarding the State from the Dangers of Subversive Elements after a U.S. activist swam across a lake to her house uninvited. The American man has also been arrested according to the U.S. State Department. The charges against Suu Kyi carry a maximum jail term of five years, which would stretch her detention past its supposed expiry date this month and beyond the 2010 elections. Suu Kyi has been under house arrest in Rangoon for most of the past 19 years since her party's victory in 1990 general elections.