He may be vital to western plans in Afghanistan but Hamid Karzai is regularly described by frustrated diplomats and foreign statesmen as erratic, emotional and prone to believing paranoid conspiracy theories.

On some occasions Karzai's own ministers accuse him of complicity in criminal activity, including ordering the physical intimidation of the top official in charge of leading negotiations with the Taliban.

In memos back to Washington, released by WikiLeaks, the current US ambassador, Karl Eikenberry, adopted a particularly weary tone when describing often bizarre meetings with the mercurial president.

In one in 2009, Karzai argued that the US intended to "divide Pakistan and weaken Afghanistan in order to pursue its fight against terrorist groups"; and suggested the US and Iran were working together to support his main political rival in the presidential elections. Eikenberry "pushed back hard" against Karzai's claim in what appears to have been a heated exchange.

Eikenberry concluded it was unlikely Karzai would ever break his habit of blaming the US and its allies for Afghanistan's troubles and not addressing his own shortcomings. "Indeed his inability to grasp the most rudimentary principles of state-building and his deep seated insecurity as a leader combine to make any admission of fault unlikely, in turn confounding our best efforts to find in Karzai a responsible partner."

Eikenberry identified two competing personalities in Karzai. "The first is a paranoid and weak individual unfamiliar with the basics of nation-building and overly self-conscious that his time in the spotlight of glowing reviews from the international community has passed. The other is that of an ever-shrewd politician who sees himself as a nationalist hero who can save the country from being divided by the decentralisation-focused agenda of Abdullah [Karzai's main rival in the 2009 election]."

Omar Zakhilwal, the much respected finance minister, told the Americans Karzai was "an extremely weak man who did not listen to facts but was instead easily swayed by anyone who came to report even the most bizarre stories or plots against him". He said an "inner circle" of top ministers had developed a system to work together to influence Karzai when he started "going astray on such matters".

Overall, "Karzai is at the centre of the governance challenge", says a briefing paper written by the embassy for Robert Gates, the US secretary of defence, in late 2008. "He has failed to overcome his fundamental leadership deficiencies in decisiveness and in confidence to delegate authority to competent subordinates. The result: a cycle of overwork/fatigue/indecision on the part of Karzai, and gridlock and a sense of drift among senior officials on nearly all critical policy decisions."

International statesmen who meet Karzai occasionally have also expressed concerns.Nursultan Nazarbayev, the president of Kazakhstan, said in a meeting with General David Petraeus last year: "Karzai is weak, but it's better to keep him on." In a conversation with John McCain in 2008, David Cameron said that "each year he had the sense Karzai's sphere of influence was shrinking".

Relations between Karzai and the British have long been strained. The cables identify the problem as a fundamental disagreement between the two sides about how best to pacify Helmand.

For Karzai the solution was to "bring the tribes to our side" by appointing a corrupt but powerful tribal bigwig as governor. The UK, on the other hand, believed clean and effective local government was the answer.

On several occasions the British thwarted Karzai's plan to replace Gulab Mangal – the technocratic governor of Helmand praised to the skies by the US and UK – with Sher Mohammad Akhundzada, a leader of the Alizai tribe who served as governor of the province from 2001 to 2005.

Once Gordon Brown had to tell Karzai that "Akhundzada was not an acceptable alternative, given his history of corruption and involvement in drug trafficking" and that Karzai was being deceived about the state of Helmand by scheming palace advisers.

British opposition created more recriminations, with a bitter Karzai telling a district governor that Helmand "is not part of my administration" but is "controlled by foreigners".

The cables reveal that Karzai first tried to reinstate Akhundzada, – described as a "known warlord and criminal" – three months after the appointment of Mangal in March 2008. There was another effort in 2009 when Karzai argued that gaining the support of Akhundzada's Alizai tribe was key to gaining stability in Helmand's most troubled districts, including Sangin and Musa Qala. Karzai argued with the US that it was better to have "a bad guy on your side" rather than him "working for the Taliban". But in its analysis the US embassy said a "key underlying calculation" of Karzai's was that Akhundzada could turn out his Alizai tribe to vote for the president in the 2009 election.

There are signs that the UK worried about Karzai's lack of public appreciation for the British effort. In November 2008 David Miliband was recorded asking Karzai to write "an open letter to the British people" designed to reassure the UK public about the "Afghan project".

Frustration with the Karzai family occasionally bubbles over among diplomats. The Canadian ambassador William Crosbie told his US counterpart in February that they must be "prepared for a confrontation with Karzai" to prevent the rampant fraud that wrecked the presidential elections happening again in this year's parliamentary poll.

He said Canada would demand that the "international community ... stand up for the silent majority or be blamed for letting Karzai and his family establish across the country the system of patronage and control that exists in Kandahar".

But perhaps the most damning accounts of Karzai's style of governing are from the president's close colleagues. In 2009 Umar Daudzai, Karzai's chief of staff, told the Americans he was "ashamed" of an incident in which Karzai pardoned five border policemen who had been caught transporting 124kg of heroin in an official vehicle.

The episode sent relations between Karzai and Washington into one of its periodic lows, with many assuming that Karzai had freed the men because their extended family had contributed to his re-election campaign. Speaking generally about the release of drug traffickers, Mohammad Daud, deputy minister of interior with responsibility for tackling illegal drugs, is quoted in a cable as telling assistant US ambassador Anthony Wayne that he had learned "some members of the president's family had been receiving money from those seeking the pardon and release of convicted traffickers".

Daud described their release as a "big psychological blow" to him and the country's counter-narcotics police force.Masoon Stanekzai, a senior government official charged with disarming militias and "reintegrating" Taliban insurgents, is reported to have feared for his own life after defying Karzai's many demands to remove two provincial election candidates from Helmand from a blacklist so they could stand.

Both were known drug traffickers and members of illegal militias.

Stanekzai told the embassy that he received threats and menacing visits to his office from the men, who on one occasion brought along a 54-man militia that Stanekzai was supposed to have disbanded.

The highly respected minister said the president himself was involved in the threats. The cable says: "Karzai himself has made no overt threats but he [Stanekzai] believes the president is behind a litany of visits Stanekzai has had by known warlords – including the two narcotics traffickers – accompanied by their private militias in the past two weeks."

The incident was "an example of Karzai meddling in the elections by using intimidation to protect known thugs".