While their spouses were busy with a bilateral meeting at the White House on Tuesday (Aug 2), Mrs Lee Hsien Loong and US First Lady Michelle Obama went on a quick tour of Washington's National Gallery of Art.

Director of the National Gallery Earl A. (Rusty) Powell guided the two women through some of the masterpieces in the gallery, including the last portrait of Abraham Lincoln without a beard and American sculptor Augustus Saint-Gaudens' Shaw Memorial.

This memorial, which commemorates the valiant efforts of Colonel Robert Gould Shaw and the men of the 54th Massachusetts, the first Civil War regiment of African Americans enlisted in the north, has been acclaimed as the greatest American sculpture of the 19th century.

There was a light moment when Mr Powell was guided out of the way of cameras and Mrs Obama put her hand behind her ear, miming inability to hear him as he moved away.

Mrs Lee and Mrs Obama also stopped for a quick performance presented by a group of students from the Turnaround Arts Summer Programme.

Later in the day, Mr and Mrs Obama will host Mr and Mrs Lee to a state dinner to celebrate the 50th anniversary of diplomatic relations between Singapore and the US.

The dinner is the first to be held in honour of a South-east Asian leader. Under Mr Obama's administration, leaders from only four other Asian countries - China, Japan, South Korea and India - have been thus honoured.

About 200 guests will dine on Maryland blue crab salad and American Wagyu beef tenderloin before enjoying a performance by singer-songwriter Chrisette Michele.

Mr and Mrs Lee will also attend a state luncheon on Tuesday, hosted by Mr Joe Biden, his wife Jill and Mr John Kerry at the State Department.

Mr Lee is on a six-day visit to the United States. He and some of the delegates are staying at the Blair House, the guest house of the US President. Other foreign dignitaries who have called it their temporary home include Britain's Queen Elizabeth II and Mr Nelson Mandela, the former South African president.