"We are open, open to discussion, but we have our own principles," the government-owned The Herald newspaper quoted him as saying at rallies on Tuesday.
"If they [the opposition] have problems they can always bring them forward."
Mugabe also called Tsvangirai, who pull out of the presidential race on Tuesday citing widespread violence and intimidation, a coward.
The MDC leader is still at the Dutch embassy in Harare where he sought refuge earlier this week following a police raid on his party headquarters, saying he feared for his life.
He told the AFP news agency that he would leave when he was "satisfied that it's safe to do so".
The opposition says that at least 80 of its supporters have been killed by Zanu-PF loyalists and another 200,000 people have been displaced in what it calls Mugabe's "campaign of intimidation" to deter people from voting.
Mugabe supporters have denied the allegations and the president taunted his opponent on Tuesday, asking: "Why seek refuge? What for? Why are you afraid of the vote now?"
Tsvangirai won the first round of the election on March 29 but did not secure the outright majority needed to prevent a second round of voting.
|Opposition supporters are worried they will be forced to vote for Mugabe [AFP]
On Wednesday, he wrote in The Guardian
newspaper that the United Nations had to go further than verbal condemnation and move on to "active isolation" which required "a force to protect the people".
"We do not want armed conflict, but the people of Zimbabwe need the words of indignation from global leaders to be backed by the moral rectitude of military force," he wrote.
"Such a force would ... separate the people from their oppressors and cast the protective shield around the democratic process for which Zimbabwe yearns."
A "new election, devoid of violence and intimidation, is the only way to put Zimbabwe right", he said.
On Monday, the UN Security Council unanimously condemned the "campaign of violence" in Zimbabwe saying it had made a free and fair run-off election "impossible".
South African Nobel peace laureate Desmond Tutu also called for international action, describing Mugabe as a "Frankenstein" figure who was holding his country to ransom.
The Anglican Archbishop of Cape Town told Australian television that Zimbabwe's best hope was an international peacekeeping force primarily comprised of Africans with non-African nations providing logistical support.
Mugabe said that Zimbabwe would resist outside interference in its affairs.
"The verdict is ours as the people of Zimbabwe," The Herald newspaper quoted him as saying.
"They can shout as loud as they want from Washington and London but our people will deliver the final verdict."
Mugabe also chided some African neighbours for not standing up for Zimbabwe.
"Not a single country has been bold enough to say that the illegal sanctions by the West should be lifted or tell them not to interfere in our internal affairs," he said.
Regional criticism of Mugabe's government has grown, with the ruling party in neighbouring South Africa issuing its harshest criticism to date.
The African National Congress said it was "deeply dismayed by the actions of the government of Zimbabwe which is riding roughshod over the hard-won democratic rights of the people of that country".
Southern African leaders are holding an emergency meeting in Swaziland on the situation, but Thabo Mbeki, the South African president and Zimbabwe mediator, was not expected to attend.
"President Mbeki was not invited to because he is not a member of the troika, but the door is open for him to attend as a mediator to the Zimbabwe crisis," Tercy Simelane, spokesman for Swaziland prime minister Absalom Themba Dlamini, said.
Speaking in New York, Boniface Chidyauskiu, Zimbabwe's ambassador to the UN, insisted that Tsvangirai was in no danger and said that reports of threats to his life were propaganda.
"Nothing has happened to him and he has been campaigning," the ambassador told AP Television, accusing the MDC of using violence and intimidation to slander the government.
"Any movement is taken out of context and is blown out of proportion. The truth of the matter is the police did not raid MDC headquarters," he said.
Chidyauskiu accused Zimbabwe's main opposition party of trying to win power "by hook or crook".
"And they are playing to the international media to say, you know, 'come and install us', you know, 'we are being persecuted'," he added.