Ayatollah Khamenei urged the government to deal with the country's economic difficulties and sustenance, to expand the country's ties with the world and to stand against all "arrogant countries, in particular the U.S".
Rouhani has vowed to open Iran up to worldwide investment and trade but the Islamic Republic insider who has held senior political and military posts since the 1979 Islamic revolution, faces enormous challenges, including deepening political divisions among the country's ruling elite and U.S. President Donald Trump's aggressive Iran policy.
Iran's supreme leader formally endorsed Hassan Rouhani as president in a ceremony broadcast on state television on Thursday, after Rouhani secured a second term in a landslide election win on May 19.
Symbolizing the endorsement, Khamenei handed over the presidential mandate to Rouhani. Following the swearing-in ceremony, the President will have two weeks to submit his new cabinet to the Parliament for the vote of confidence.
Rohani, a 68-year-old self-proclaimed moderate, won a second term in May.
President Rouhani underlined that Joint Comprehensive Plan of Action (JCPOA) indicated Iran's good will for effective and constructive interaction at worldwide level.
However, his inauguration came less than 24 hours after fresh sanctions were imposed by US President Donald Trump, who has threatened to tear up the nuclear deal entirely.