Benazir Bhutto has asked Britain and America to help to investigate the most deadly suicide bombing in Pakistan to date, which struck her convoy at midnight on Thursday, casting a deep shadow over her return to the front line of Pakistan politics.

The former Prime Minister, speaking to The Times at her family compound in Karachi, said that she had no confidence in the official investigation. She blamed “elements within the Government” but not President Musharraf for the twin blasts that killed 140.

“I have discussed this with diplomats of some countries, including Britain,” she said, calling for “an independent and impartial inquiry into all aspects of the assassination attempt”. She added: “We want the Government of Pakistan to seek the assistance of the international community” in sending those “who have the technical expertise to investigate crimes of this nature”. Ms Bhutto said that the attack had been made possible by sabotage of the street lights, and that the inquiry should focus on why they were turned off “for hours and hours”.

All those on her armoured campaign lorry “were worried the moment the lights went out”, she said. “Our guards were looking out for someone who was bulky. The bomber always has to be bulky.”

Ms Bhutto denied that she had been mistaken to hold a ten-mile procession from the airport to the heart of Karachi to greet her triumphant return from eight years of exile under threat of corruption charges. The crowd, estimated at a million, had been drummed up by local sponsors of her Pakistan People’s Party (PPP), who brought supporters in buses and trains from across the country.

But despite the immediate wave of sympathy for her some criticised her decision to put her supporters at risk, as well as herself, from an attack that she said she had been told was coming. Nasreen Jalil, the deputy mayor of Karachi, a longtime political opponent of Ms Bhutto whose own party is now in uneasy alliance with the PPP, told The Times that she thought it had been “foolhardy to have such a long procession, going so slowly. It was inviting trouble”. Ms Bhutto “didn’t have to have this show of strength. She can carry on her campaign without making it showbiz.”

Ms Bhutto acknowledged that “obviously we have to modify our campaigning to some extent but we are not going to stop our campaign to reach the people”. Yesterday, in an attempt at a secret visit that was immediately picked up by television, she spent 15 minutes at the main hospital in Karachi and visited Lyari, a very poor neighbourhood and party stronghold. Early in the morning streets there were blocked with bricks and burning tyres but supporters denied that she had failed, in two spells as prime minister, to improve their conditions. “She didn’t have enough time,” one said. “Next time, she will.”

“I feel exhausted after the last few days and nights,” Ms Bhutto said, before going to the courtyard to lead prayers with 150 grieving widows, daughters and sisters. But she added that she may soon go to Larkana, her family home in southern Sindh province, and to Islamabad, where she may meet President Musharraf.

She called on him to appoint a new head of the investigation. She said that Manzoor Mughal, the man currently in charge, “was one of the officers at the police centre in Karachi when my husband was brutally tortured and nearly died in 1999”.

Ms Bhutto, who has given the President the names of three officials who she believes plotted to kill her, said that she had “not gone public because I don’t want this to cloud my relations with the Government”. A controversial power-sharing deal with President Musharraf, in which he extended her an amnesty against corruption charges, enabled her return.

Pressed on whether she would back the return of Nawaz Sharif, the former Prime Minister who was deposed by President Musharraf in a 1999 military coup, Ms Bhutto said that she was “personally in favour of all political personalities being able to campaign within Pakistan” for elections in January. “But his situation is complicated,” she said of the only rival who could conceivably defeat her. Mr Sharif was deported to Saudi Arabia by President Musharraf when he attempted to return last month “and it is for him to resolve” with the Saudi and Pakistani governments, she said. But she appreciated him making the first call to her after the blasts, soon after 1.30am on Friday, when she reached her residence, Bilawal House.

She will stay in Pakistan “for most of the time” until the elections, she said, but her “husband will stay abroad because he is not well” (he has had heart problems). He is staying to support her two daughters and son, now at the University of Oxford, where she also studied.

Ms Bhutto said that she was not impressed by the use that President Musharraf had made of US funds in tackling terrorism, saying that the violence had soared and that Islamic fundamentalists presented a “very serious threat” that could be countered only by restoring democracy.

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