Ban Ki-moon noted a "lack of progress" in UN special envoy Ibrahim Gambari's trip to Myanmar, where he is attempting to end the country's political crisis and promote democratic reform.
Earlier, Myanmar's military junta summoned foreign diplomats to its new remote capital to meet with Gambari, diplomats said.
The diplomats were asked to meet him in Naypyitaw, where he has been holding talks with Cabinet ministers but has yet to meet with powerful junta leader Senior General Than Shwe.
"He (Gambari) has not been able to meet with Senior General Than Shwe and I understand he is meeting madame Aung San Suu Kyi tomorrow - Wednesday," Ban told reporters at UN headquarters in New York.
"I'm concerned at this time about the lack of progress," he said.
Ban said he has instructed Gambari not only to launch a dialogue between Suu Kyi and Myanmar's political leadership but also to press for the release of all detained monks, students and demonstrators and to press the government to take necessary "democratic measures".