Iran's reformist ex-president Mohammad Khatami on Sunday endorsed President Hassan Rouhani in a video message, calling on voters to give him another term in this week's election.

"Mr Rouhani's government has been a successful one, despite all the limitations, problems and the great expectations," he said in the video posted on social media.

"We should all go and vote for Rouhani, for freedom in thought, logic in dialogue, law in action, securing the rights of citizens and enforcing social and economic justice."

Khatami praised the government for taming rampant inflation of above 40 percent in 2013 to below 9.5 percent and the "steps" taken against stagnation.

Unemployment has increased in the past four years from 10.5 percent to 12.5 percent, while youth joblessness stands at 27 percent.

"Many issues have been resolved but bigger issues remain, which we must all help to solve," he said in the video published on his Telegram messenger account.

Khatami, the de facto leader of the reformist camp, has been under a media ban during the past few years for supporting the Green Movement protestors in the 2009 presidential election that saw hardliner Mahmoud Ahmadinejad re-elected.

In 2016, he released a video that played a crucial role in helping pro-Rouhani candidates to defeat ultra-conservatives in parliamentary and Assembly of Experts elections.

The video became well-known for his use of the phrase "I repeat".

"This time, it is you who should repeat. Repeat the vote for dear Rouhani, to boost hope for future," he said on Sunday, referring to Friday's presidential election.

In 2013, Khatami helped Rouhani take office by convincing reformist Mohammad Reza Aref to step aside in Rouhani's favour.

It is yet to be seen if Khatami does the same in this election to the reformist First Vice President Eshaq Jahangiri who is running alongside Rouhani.

Khatami also warned people against being deceived by "baseless promises" from Rouhani's conservative rivals who have vowed to increase cash handouts and create millions of jobs in four years.