Monday's ceremony displayed the deep political divides confronting Ahmadinejad, as two former presidents boycotted the event -- Akbar Hashemi Rafsanjani and Mohammad Khatami -- as well as defeated pro-reform candidates Mir Hossein Mousavi and Mahdi Karroubi, reported state media.
In addition, no one from the family of Ayatollah Ruhollah Khomeini, leader of the 1979 Islamic revolution, attended, according to the Associated Press.
Khamenei described the election as a "golden page" in Iran's political history and said it was a "vote for the fight against arrogance and brave resistance to the international domination-seekers" -- a clear reference to the United States and its allies -- according to comments quoted by state TV, reported the AP.
The landslide victory of Ahmadinejad in the June 12 election sparked weeks of protests in Tehran streets and abroad, and prompted calls of fraud from the opposition candidates.
After reviewing the opposition candidates' complaints, Iran's Guardian Council reported in late June that it found "no major fraud" in the election and would not annul the results.
Still, scattered protests have continued in the country, and some tactics recall the Islamic revolution, such as opposition supporters shouting Allahu Akbar from rooftops during the night and protesters using funerals and 40-day memorials for slain demonstrators as rallying points.
An opposition Web site reported clashes Monday afternoon between protesters and special forces in north Tehran's Vanak Square, the AP reported. Iranian authorities have barred foreign media from covering street protests.
Ahmadinejad faces several challenges in his second, four-year term as president, including assembling a cabinet acceptable to the mostly conservative parliament, which may object if he merely picks members of his inner circle, according to Reuters.
He also faces a September deadline, posed by President Barack Obama, to show a willingness to open a dialogue on its nuclear ambitions and other key issues.
Ahmadinejad has shown little concession on Iran's nuclear program, which he insists is for civilian energy purposes only, while the United States and its allies contend it could lead to atomic weapons.
In a July 16 speech, Ahmadinejad reiterated that Iran will proceed with its nuclear program and would become a world power that "will bring down the global arrogance" -- a phrase often used for the United States, news organizations reported.
---- Compiled from wire reports and other media sources