PARIS — President Nicolas Sarkozy, who promised voters “a republic beyond reproach,” came under mounting pressure Tuesday from allies as well as opponents over allegations that he and his campaign organization took illegal cash donations from France’s richest woman.

The accusations, made to police and posted on a website by the heiress’ former accountant, constituted the potentially most damaging chapter in a string of scandals involving Sarkozy’s government and 87-year-old Liliane Bettencourt, who owns the L’Oreal cosmetics firm.

The opposition Socialist Party’s general secretary, Martine Aubry, called on Sarkozy to explain himself and said France was “confronting a major crisis of confidence.” At the same time, Jean-Francois Cope, who leads Sarkozy’s ruling coalition in parliament, said Sarkozy should “speak to the French people” to bring the crisis under control and allow the country to focus on its economic problems.

But Sarkozy declined to address the allegations directly. In an appearance at a health facility, he instead decried those who he said were diverting attention from essential issues such as health care to wallow in “horror and calumny that has only one goal, to soil others without any kind of reality.”