A US terror alert issued this week about al-Qaida plots to attack targets in western Europe was politically motivated and not based on credible new information, senior Pakistani diplomats and European intelligence officials have told the Guardian.

The non-specific US warning, which despite its vagueness led Britain, France and other countries to raise their overseas terror alert levels, was an attempt to justify a recent escalation in US drone and helicopter attacks inside Pakistan that have "set the country on fire", said Wajid Shamsul Hasan, the high commissioner to Britain.

Hasan, a veteran diplomat who is close to Pakistan's president, suggested the Obama administration was playing politics with the terror threat before next month's midterm congressional elections, in which the Republicans are expected to make big gains.

He also claimed President Obama was reacting to pressure to demonstrate that his Afghan war strategy and this year's troop surge, which are unpopular with the American public, were necessary.

"I will not deny the fact that there may be internal political dynamics, including the forthcoming midterm American elections. If the Americans have definite information about terrorists and al-Qaida people, we should be provided [with] that and we could go after them ourselves," Hasan said.

"Such reports are a mixture of frustrations, ineptitude and lack of appreciation of ground realities. Any attempt to infringe the sovereignty of Pakistan would not bring about stability in Afghanistan, which is presumably the primary objective of the American and Nato forces."

Dismissing claims of a developed, co-ordinated plot aimed at Britain, France and Germany, European intelligence officials also pointed the finger at the US, and specifically at the White House. "To stitch together [the terror plot claims] in a seamless narrative is nonsensical," said one well-placed official.

While Abdul Jabbar, a Briton, and others killed by an American drone strike on 8 September in North Waziristan, in Pakistan's tribal areas, were heard discussing co-ordinated plots, including possible "commando-style" attacks on prominent buildings and tourist sites in European capitals, security and intelligence officials said the plots were nowhere near fruition.

The officials did not deny the men, and other foreign-born jihadi recruits who travel to the tribal areas for indoctrination and training, represented a potentially serious threat. "You have discussions about all sorts of things – that does not necessarily mean there is anything concrete. It is not easy to set up groups," said one counter-terrorism official.

By making it clear that the US drone strikes were pre-emptive, and were not in any way combating an imminent threat, European officials raised fresh questions – this time directly involving a British national – about the legality of the attacks, which could be viewed as assassinations.

They said Washington was the "driver" behind claims about a series of "commando-style" plots and that the CIA – perhaps because it was worried about provoking unwelcome attention to its drone strikes – was also extremely annoyed by the publicity given to them.

The plot claims, which western intelligence agencies were aware of for months, were leaked last week to the American media.

They were followed by a spate of what security and intelligence officials said were exaggerated claims in the British media, a US state department warning to American citizens to be vigilant when visiting Britain, France, and Germany, a "tit for tat" warning by France to its citizens visiting the UK, and alerts issued by the Swedish and Japanese governments.

Thomas de Maizière, Germany's interior minister, publicly expressed his scepticism about the US terror warning, saying he saw no sign of an imminent attack on Germany. He described the danger to Germany as "hypothetical".

The sharp rise in US unmanned drone attacks in Pakistan's tribal areas, coupled with several cross-border raids by American helicopter gunships that culminated in the killing of two Frontier Corps soldiers last week, was destabilising Pakistan, Hasan said.

"Why are they putting so much pressure on us? It is a threat to the democratic system … But people in Pakistan feel Washington does not care." American actions were "obviously" linked to Obama's decision to set a timetable for leaving Afghanistan. The US leader had "jumped the gun" and now "the Americans are in a hurry".

He said fears were growing in Pakistan that the US was planning a bombing campaign using fixed-wing aircraft as well as drones in North Waziristan.

Hasan said Washington politicians failed to understand how much the US needed Pakistan in the "war on terror". Nor did they realise that public anger over repeated US infringements of Pakistani sovereignty could boil over into attacks on American personnel and interests that the government might not be able to control.

"The government does not want to go down this road," he said. "But people feel abused. If they [the Americans] kill someone again, they will react. There is a figure that there are 3,000 American personnel in Pakistan. They would be very easy targets."

Hasan said American personnel stationed at the Pakistani air force base at Jacobabad, on the border between Sindh and Baluchistan provinces, could be vulnerable if the situation deteriorated further. The US requested the use of Jacobabad, and other bases at Dalbandin and Pasni, after the 9/11 attacks, and has maintained a military presence there ever since.

Another Pakistani diplomat said Jacobabad was the main centre of operations for CIA and US army drones, which are ultimately controlled from America. "They have hangars there. That's where they fly from and that's where they return."

The drone operations began in June 2004 with the tacit, reluctant agreement and involvement of the Pakistani authorities but were now in effect running beyond Pakistan's control, the diplomat suggested. "We have always denied it in the past. But everybody knows this is happening. We need to wake up," the official said.

A US official said: "Our allies have been briefed on the nature of the threat and the intelligence that led to the travel alert and everyone understands this cannot be taken lightly.

"To try to ascribe any political motivation is misguided and irresponsible."