In this day and age, demands by an American president for a nasty foreign regime to change its ways or step down are nothing new.

But when first ladies set aside their presumed role of supervising placements at White House state dinners and airing worthy platitudes about women's causes, to launch a media blitz against a brutal military junta, then eyebrows are raised. And so it is now, as Laura Bush conducts her own diplomatic offensive against the indubitably unpleasantgovernment of Burma.

In the aftermath of the crackdown on protests that had been led by Buddhist monks on the streets of Rangoon, Mrs Bush has been ever more visible and vehement in her denunciations. The other day, the BBC found itself invited for a rare interview with the First Lady on that subject. Yesterday, her campaign took on even larger dimensions, with a Laura Bush op-ed in the Wall Street Journal, and a simultaneous front-page interview with the country's biggest selling newspaper, USA Today.

"First Lady: Burma has 'Days' to Act," screamed the USA Today headline. Her tone in the WSJ was no less trenchant. "General Than Shwe [the leader of the junta] and his deputies are a friendless regime," she wrote. "They should step aside to make way for a unified Burma governed by legitimate leaders."

Yesterday Anita McBride, Mrs Bush's chief-of-staff, explained that, for several years, the First Lady had been deeply concerned by events in Burma, after having read Freedom from Fear, written by Aung San Suu Kyi, the leader of the country's democracy movement who has been under house arrest for 12 of the past 18 years. "Mrs Bush wants to use her platform as First Lady," she explained.

In USA Today, Mrs Bush, who seemed the embodiment of a demure former librarian and teacher when she moved into the White House in 2001, admitted that initially she expected her role to be "totally domestic". On Burma, "my influence is really in being able to shine a spotlight on human rights situations that I want the American people to look at." Her chief-of-staff insists that concern extends to US allies as well as enemies. Mrs Bush will also have something to say during her upcoming visit to US friends in the Middle East and Gulf.

Mrs Bush is far from the first presidential spouse to speak out on foreign policy. Indeed, she cites the example of Lady Bird Johnson, another activist first lady who once noted that "although elected by one man only," a presidential spouse, if she wanted to use it, had a very effective public podium.

And many have – most notably perhaps Eleanor Roosevelt among 20th century first ladies. Others before and after have left their own small diplomatic marks, such as Edith Wilson who accompanied her husband, Woodrow, to Europe for peace talks after the First World War. More recently, Rosalynn Carter represented the US at a summit with Latin American leaders, while Hillary Clinton created waves in 1995 by rebuking China for its record on human rights in a speech in Beijing.

Oddly, the one recent first lady who was not involved with a specific foreign cause was Laura's mother-in-law Barbara, wife of the first President Bush.

Laura's interventions, however, now make eminent sense. The sheer rarity of a first lady's embrace of a foreign cause lends impetus. While her husband's approval ratings plumb near-record depths, she remains highly popular. After Guantanamo Bay, the Iraq war and the controversy over US use of torture, George Bush's credibility as a champion of human rights has been severely damaged.

However the practical consequences of the move may be limited. Mrs Bush's public involvement with the democratic cause in Burma began last year, when she led an international round table at the United Nations on the crisis.

Now, and thanks largely to prodding by Mrs Bush, the UN envoy Ibrahim Gambari will soon be returning to Burma. Mrs Bush also indicated that her husband will soon be imposing tighter US government sanctions.