Mugabe hopes to find regional backing in Malawi
He was speaking in Malawi, where he has arrived for a regional conference at which he hopes to rally support in the run-up to elections in March.
The Commercial Farmers' Union (CFU) says that another 23 landowners have been forced from their homes in the past week, as a new campaign against white-owned farms begins.
Mr Mugabe will attend a summit meeting of the Southern African Development Community (SADC) in the Malawian commercial capital, Blantyre, on Monday.
On his arrival, he said: "Britain has a war with us, [Prime Minister Tony] Blair wants his own version of colonialism in Zimbabwe and we will resist that."
On Friday the European Union gave Harare a week to accept foreign media and international monitors.
But the government said it would allow international observers to witness the elections but not to monitor them.
Speaking after a day of intense talks with representatives of the European Union, Zimbabwean Foreign Minister Stanislav Mudenge said he would issue invitations to observers shortly.
But opposition candidate for president, Morgan Tsvangirai, said President Mugabe could not afford to reject the monitors.
"He has no option but to allow an international assessment of the election to give it legitimacy. He needs that legitimacy."
Farm attacks reported
The looting of white-owned farms reported by the CFU took place mainly around Raffingora, about 100 kilometres (60 miles) north-east of Harare.
One farmer was given five minutes to leave his property, said Jenni Williams, a CFU spokesperson.
She said that militants had told farmers that they were responsible for sanctions imposed by the United States and threatened by the EU.
Opposition politicians say that the ruling Zanu-PF party has a training camp in the Raffingora area, where it drills unemployed youths into a militia force.
International criticism
EU foreign ministers are due to review progress in Zimbabwe at their next meeting in Brussels in late January, but there has been no mention of the action that might be taken if Harare fails to provide a satisfactory response to concerns about the elections.
Further criticism of Zimbabwe has come from the United States, which said the authorities were trying to intimidate opposition supporters.
US State Department spokesman Richard Boucher said five opposition supporters had been killed in the past two weeks, and there was little prospect of the murders being investigated.
And South Africa described as unacceptable an army statement indicating it would not accept an election victory by the opposition.
The Zimbabwean parliament has just approved new legislation banning independent monitors, and is expected next week to push through a bill on control of the media.