Nicolas Sarkozy is facing an unprecedented revolt by French diplomats who warn that his foreign policy gaffes have left France pathetically diminished on the world stage.

After weeks of embarrassing French slip-ups – including Paris blindly standing by the Tunisian and Egyptian dictatorships until the last minute – a group of diplomats have published a scathing attack on the president in Le Monde.

The anonymous letter from serving and former diplomats warns: "France's voice in the world has disappeared." They accuse Sarkozy of amateurism, acting on impulse, ignoring ambassadors and caring more about how he looks on TV than the fundamentals of foreign affairs.

They claim France risks losing its footing on the world stage and becoming insignificant. "Africa escapes us, the Mediterranean snubs us, China has crushed us and Washington ignores us!" the letter says.

The timing of the diplomatic rebellion is particularly damaging: Sarkozy is the current president of the G8 and G20 economic forums and is preparing for a re-election bid next year.

The uproar is serious, given the importance of foreign affairs in defining French national pride and the president's domestic popularity.

France has the second biggest diplomatic network in the world, after the US.Since Charles de Gaulle, France has boasted of its unique and independent stance in world diplomacy and foreign policy is the exclusive personal domain of the president. French leaders have traditionally used the world stage to boost their domestic standing, with Jacques Chirac conveniently using his popular opposition to the Iraq war to mask his failings at home.

But a poll for the newspaper Libération this week found 72% of French people think their country's image in the world has deteriorated since Sarkozy became president in 2007.

French diplomacy is struggling to recover from its mishandling of the popular uprisings in the Arab world and cosy business and arms ties to authoritarian regimes. During the brutal repression of the Tunisian revolution, the French foreign minister, Michele Alliot-Marie, offered the "savoir faire" of French police to help the regime. It emerged that mid-revolt, she and her parents stayed with, and did business with, a crony of the dictator Zine al-Abidine Ben Ali.

Alliot-Marie, who has refused to quit, is now so loathed in the former French colonial protectorate that the Tunisian foreign minister was forced to resign for saying he respected her.

Embarrassingly, Britain's foreign secretary, William Hague, beat the French government to be the first European political heavyweight to visit post-revolution Tunisia. When French ministers finally arrived this week, Alliot-Marie was not with them.

The embarrassment was compounded last weekend when hundreds of Tunisians took to the streets demanding the departure of the new French ambassador, Boris Boillon, a "Sarkoboy" and presidential protege parachuted in after Sarkozy sacked the previous ambassador for failing to predict the revolution.

Boillon, 41, once referred to by Sarkozy as "my little Arab" because he speaks Arabic, was forced to deliver a humiliating apology on Tunisian television after being filmed throwing a Sarkozy-style tantrum and insulting local journalists who asked him about his inexperience.

Unnamed ambassadors briefing the press have complained about Sarkozy's personality. One told Libération that French foreign policy, like Sarkozy, had become "agitated, impulsive, ideologically incoherent and contradictory". Diplomats complained the Elysée sidelined and ignored its diplomats over the Arab uprisings.

Talking to foreign journalists, Sarkozy's chief diplomatic advisor, Jean-David Levitte, said of the diplomats' revolt: "I don't like anonymous letters."

He insisted that ambassadors were not being ignored, saying: "I read 150 diplomatic cables a day. It's my daily bread."

The Socialist leader, Martine Aubry, told French radio: "Today it's clear that French diplomacy no longer exists; we're confusing contracts with diplomacy and that's why France is shrinking in the world. Its voice no longer carries."

French diplomats' resentment of Sarkozy had been growing under his previous foreign minister, the leftwing former humanitarian champion, Bernard Kouchner, who was dubbed Mr Know It All by foreign office staff who complained that he was arrogant.