Around 330 villages have also been badly damaged by the quake, local officials say.
The epicentre of the quake was in a mountainous area between the two industrial cities of Boroujerd and Doroud.
Three tremors struck the remote region, the largest of which measured 6 on the Richter scale.
The initial quake of magnitude 4.7 struck late on Thursday evening, according to state television.
It was followed by a quake of magnitude 5.1 at 11:06 pm local time while the third much stronger magnitude 6 quake struck at 4:47 am local time on Friday.
The quake damaged buildings in rural areas and cut telephone lines.
Iranian television showed brick houses flattened, with bent iron girders poking out, and mud buildings reduced to mounds of dust.
Families come to terms with the
Ali Barani, a local official, said several of the hardest hit villages in the region had been flattened by the quake.
Mahmoud Ahmadinejad, Iran's president, ordered emergency relief to be sent to the quake zone, the official IRNA news agency reported.
The US is also prepared to offer humanitarian assistance to Iran, Condoleezza Rice, the US secretary of state, said while on a visit to the UK.
The quake caused panic, sending residents of Doroud running from their homes. Many spent the night in out in the open fearing further aftershocks, residents said.
Major quakes since 2000
2005: At least 74,000 people are killed when a quake measuring 7.6 strikes Kashmir.
2004: Over 200,000 die across Asia when an 8.9 magnitude quake triggers a tsunami.
2003: Over 26,000 are killed in when the Iranian city of Bam is destroyed by a 6.6 level quake.
2003: Around 2,000 people die in a quake measuring 6.7 that hits northern Algeria.
2001: Around 20,000 are killed when the Indian state of Gujurat is hit by a 7.9 level quake.
"We are afraid to get back home. I spent the night with my family and guests in open space last night," said Mahmoud Chaharmiri, a resident of Doroud.
In February 2005, a 6.4-magnitude quake rocked the town of Zarand in southern Iran, killing 612 people and injuring more than 1,400.
A quake registering 6.6 destroyed the historic south-eastern city of Bam in the same region in December 2003, killing 26,000 people.
Iran is on several seismic fault lines and is prone to earthquakes. It experiences at least one small earthquake a day on average.