Thein Sein met today with members of the Senate and House, a day after he became the first Myanmar leader to visit the White House in five decades.
As Myanmar has shifted from military rule in the past two years, it has freed hundreds of political detainees but others are still held.
House Democratic leader Nancy Pelosi and three other Democrats handed Thein Sein a prisoner list and called for an end to attacks on minorities.
President Barack Obama voiced strong support yesterday for Thein Sein's leadership, but said violence against minority Muslims needs to stop.