The United States has raised concerns in the past about Iran's satellite programme, describing the launch of a carrier rocket in January 2019 as a "provocation".
"Beginning countdown to launch #Zafar_Satellite in the next few hours... In the Name of God," Mohammad Javad Azari Jahromi wrote on Twitter.
On February 1, the head of Iran's space agency said the 113-kilogramme Zafar -- Victory in Farsi -- would be launched into orbit 530 kilometres (329 miles) above Earth by a Simorgh rocket.
Its "primary mission" would be collecting imagery, Morteza Berari told AFP, adding that Iran needed such data to study earthquakes, deal with natural disasters and develop its agriculture.
In January 2019, Tehran announced that its Payam -- Message in Farsi -- satellite had failed to reach orbit, after authorities said they launched it to collect data on the environment in Iran.
The US said the launch of the carrier rocket was a violation of a 2015 UN Security Council resolution which endorsed an international accord on curbing Tehran's nuclear programme.
Resolution 2231 called on Iran to refrain from any activity related to ballistic missiles capable of delivering nuclear weapons.
Iran maintains it has no intention of acquiring nuclear weapons, and says its aerospace activities are peaceful and do not violate the security council resolution.
Tehran confirmed in September that an explosion occurred at one of its satellite launch pads due to a technical fault, and slammed US President Donald Trump for "gleefully" tweeting about it.
Replying to a tweet that asked what if Zafar fails like it predecessor, Jahromi said "we will try again".
Iran's internet services have faced cyber attacks for the past two days, according to the ministry. Officials have not elaborated on the source of the attack or its likely motives.