"We appeal to foreigners and external forces to leave the resolution of the Zimbabwe situation to Zimbabweans alone," Chinamasa told the state-run Herald newspaper, the country's chief propaganda organ.
"Britain, the US and the EU, in particular, should stop meddling in our affairs."
The group of eight industrial powers, at a meeting on the sidelines of the summit, were to urge African leaders to pile pressure on Mugabe over the violence-wracked vote boycotted by Morgan Tsvangirai, leader of the opposition Movement for Democratic Change (MDC).
Ban Ki-moon, the UN secretary general, urged Zimbabwe's parties on Monday to restore the "rule of law" and said he would take up the crisis with African leaders.
Speaking to the AFP news agency on his plane as he arrived in Japan, Ban said Mugabe's election lacked legitimacy.
Gordon Brown, the British prime minister, told Yasuo Fukuda, his Japanese counterpart, it was "important to send a strong message to secure democracy in Zimbabwe", a Japanese government official said.
|Gordon Brown said secure democracy in Zimbabwe is needed [AFP]
Meanwhile, Angela Merkel, the German chancellor, said new sanctions were to be discussed.
After meeting with African leaders on Monday, Bush sought to show solidarity with Zimbabweans while criticising Mugabe, 84, who has ruled the country since independence in 1980.
"I care deeply about the people of Zimbabwe. I am extremely disappointed at the election, which I labelled a sham election," Bush said with Jakaya Kikwete, the Tanzanian president who is the current chairman of the AU.
Kikwete's comments, however, highlighted the West's difficulties in pressuring Mugabe, with the Tanzanian leader reiterating the AU's relatively mild call for dialogue.
"I want to assure you that the concerns you have expressed are indeed the concerns of many of us on [the] African continent," he said, adding that "the only area that we may differ is on the way forward".
"We are saying no party can govern alone in Zimbabwe and therefore the parties have to work together, come out to work together in a government and then look at the future of their country together," said Kikwete.
At a summit last week, African Union leaders called for dialogue in Zimbabwe and the formation of a national unity government.
Unit government rejected
Tsvangirai has rejected a unity government, saying it does not reflect the people's will and accommodates Mugabe after much of the world dismissed his re-election as a farce.
The talks at the G8 come after a weekend meeting between Mugabe and Thabo Mbeki, the South African president, who is the regionally appointed mediator for the crisis.
A breakaway MDC opposition faction also attended the talks, but Tsvangirai refused to meet Mbeki, who has faced criticism over his quiet diplomacy approach.
Chinamasa said Western powers were trying to wreck chances of a negotiated settlement.
"It is very evident that their hand is involved and complicating the smooth dialogue between Zanu-PF and the two MDC formations," he said, referring to the ruling party.
Tsvangirai pulled out of the run-off five days before the poll, citing rising violence against his supporters that left dozens dead and thousands injured.
His party also faced major obstacles in campaigning, with rallies barred and the MDC's number two leader, Tendai Biti, jailed on treason charges.
Biti, who was released on bail on June 26, appeared in court again on Monday and was told to return for another hearing on August 27.
Tsvangirai finished ahead of Mugabe in the March 29 first round of the election, but with an official vote total just short of the outright majority needed to secure the presidency.