Officials in Tsvangirai’s office said that he “has previous engagements in the region”.
Tsvangirai is President Robert Mugabe’s partner in the country’s 14 month-old coalition government.
Officials said he would be in South Africa and in Botswana.
Tendai Biti, finance minister and Tsvangirai’s closest aide in the Movement for Democratic Change (MDC) is also out of the country. It was possible that lesser MDC officials would attend a state banquet for Ahmadinejad on Thursday night, officials said.
The MDC has been reportedly angered by Mugabe’s invitation to Ahmadinejad.
In addition to Tehran’s disputed nuclear programme, they point to his suspect victory in elections in June last year, which sparked demonstrations in which several protestors were killed.
Some party members say the election mirrors what the MDC suffered in a presidential run-off election in 2008 when scores of its supporters were killed by Mugabe party loyalists.
Ahmadinejad is due to open a tractor factory and inaugurate a joint Iranian-Zimbabwean investment company, and is the guest of honour of the annual Zimbabwe International Trade Fair on Friday in the western city of Bulawayo.
According to the official programme, Iranian companies accounted for the bulk of foreign exhibits.
After Zimbabwe, he will continue his visit in Uganda, where he is seeking support from President Yoweri Museveni’s government against increased sanctions threatened by the United Nations Security Council. Uganda is a temporary member of the security council. SAPA