A member of the US-appointed occupation administration confirmed the cleric was still in the Shia pilgrimage city on Thursday awaiting a UN mission that will review his political demands.
His spokesman and Governing Council member, Muwaffaq al-Rubai, confirmed Wednesday's assassination attempt but said little else other than that al-Sistani is "safe and sound".
Sistani's bureau in Najaf also confirmed that the cleric was well.
Speaking to Aljazeera, al-Rubai said: "We are not astonished that Ayat Allah Sayyid Ali al-Sistani, the revered Shia cleric, should be a target … he is calling for democracy and rebuilding a new Iraq."
Last October, a similar assassination attempt was made when unknown assailants attacked with machine guns and hand grenades.
It was not clear who was behind the attempts on the cleric's life, as sectarian clashes, resistance operations and attacks on civilian targets have been a common occurrence since April.
The death of Ayat Allah Muhammad
Baqir al-Hakim outraged thousands
In September 2003, Shia cleric Ayat Allah Muhammad Baqir al-Hakim – the former leader of the Supreme Council for the Islamic Revolution in Iraq – died in a Najaf car bombing along with 80 of his followers.
Elsewhere in Iraq, a US soldier was killed on Thursday when four mortars struck a logistics base near Baghdad's airport. The attack also wounded another marine.
Aljazeera's correspondent in Baghdad reported that an Iraqi citizen was killed on Thursday when a US military convoy, which had come under rocket attack by unidentified assailants, opened random fire at his car.
"The Iraqi citizen was driving his car on the highway in al-Amiriyah district when he was shot dead.
Witnesses at the scene said the firing had damaged a mosque and the frontages of neighbouring houses.
The fatality raised the total number of US troops killed in Iraq to 529, 369 in combat and 160 in non-combat deaths.
Unofficial war estimates put the Iraqi military toll at between five and six thousand, while a website run by academics and peace activists, www.iraqbodycount.net, puts the number of civilian deaths at around 9000.