Hillary Clinton has questioned the mental health of Cristina Kirchner and asked US diplomats to investigate whether the Argentinian president is taking medication to help her "calm down".

The US secretary of state painted Kirchner as a volatile and emotional leader who suffered from "nerves and anxiety", according to a secret cable sent to the US embassy in Buenos Aires.

Clinton asked diplomats a series of questions in December last year which could infuriate Kirchner and sabotage a recent rapprochement between Argentina and America.

In a section headed "mental state and health" she asked how the first lady-turned president was managing "her nerves and anxiety" in a blunt tone which suggested US concerns.

"How does stress affect her behaviour toward advisers and/or her decision-making? What steps does Cristina Fernandez de Kirchner or her advisers/handlers take in helping her deal with stress? Is she taking any medications?

"Under what circumstances is she best able to handle stresses? How do Cristina Fernandez de Kirchner's emotions affect her decision-making and how does she calm down when distressed?"

The cable appeared to have been prompted by diplomatic spats which, according to the US embassy, showed Kirchner's government "to be extremely thin-skinned and intolerant of perceived criticism".

Clinton's queries are likely to upset the president and prompt jokes about tranquilisers in the Casa Rosada. The leaked memo comes at a sensitive time, after a thaw in relations between the two countries and the death of Kirchner's husband, Néstor.

The 57-year-old leader is known for glamour, a combative style and leftist populism which has prompted bitter clashes with foes at home and, on occasion, with the US. Her critics will seize on the memo as evidence that she is unstable. Supporters will brand it proof she has stood up to a superpower which once considered Latin America its backyard.

Clinton's preoccupation may stem partly from the fact that Kirchner's career has mirrored her own: both are lawyers and tough political operators whose husbands became president and campaigned for their wives to inherit the sash after they left office. Before being elected in 2007 Kirchner welcomed the comparisons and called the then New York senator an inspiration.

Clinton also expressed curiosity about the relationship of Argentina's power couple. "We are currently preparing a written product examining the interpersonal dynamics between the governing tandem. We have a much more solid understanding of Néstor Kirchner's style and personality than we do of Cristina ... and would like to develop a more well-rounded view of (her) personality."