Tanzania's new President Jakaya Kikwete has been sworn in after winning 80% of the votes in elections last week.
Many regional leaders including President Mugabe attended the ceremony
The general election was described by international observers as well run.
Mr Kikwete served for 10 years as Tanzania's foreign minister, after retiring from the military with the rank of lieutenant-colonel.
He says his biggest concern is to try to resolve tensions in the islands of Zanzibar, where the opposition has considerable support.
Thirteen African heads of state witnessed his swearing in.
President Kikwete inherits a country whose economy is growing at a rate of 6% a year and which is politically stable.
In his inauguration speech, he said he would continue the free-market policies of the outgoing president, Benjamin Mkapa, adding that he will make improving relations with the semi-autonomous islands of Zanzibar a priority.
"Those who expect radical changes in policy and direction are mistaken and lost. The government of the fourth republic will build on what was undertaken by previous governments and will continue with all good things," he said.
An opposition candidate filed a suit on Monday claiming electoral fraud but Mr Kikwete said he was confident "there was no foul play".
Jakaya Kikwete says he does not believe there was any rigging
Despite the legal challenge by Labour Party candidate Augustine Mrema, National Electoral Commission head Lewis Makame declared on Tuesday that Mr Kikwete had won the election and would become Tanzania's next president.
Mr Mrema, who won less than 1% of the vote according to official figures, said the poll had been rigged.
Mr Kikwete's nearest rival, the CUF's Ibrahim Lipumba, took 11.6% of the vote and also alleged fraud but did not produce any evidence to back up his claims.
The governing Chama Cha Mapinduzi (CCM) party also retained its overwhelming majority in parliament, with 206 out of 232 seats.
Mr Kikwete, 55, takes over from Mr Mkapa, who has stepped down after two terms.
Turnout was 72% of the registered voters with 11.3 million votes cast.