Speaking at a news conference in Kabul on April 3, Rabbani said the government's failure to solve the country's problems was a reason behind the formation of the United National Front of Afghanistan.
"The weakness of the government in solving crises and the emergence of corruption are serious threats to state security," he said. "Watching this situation, a group of parties and politicians decided not to remain on the sidelines regarding solutions to national problems anymore. So they decided to create a means of cooperation by forming the United National Front and starting joint work."
Rabbani also said the new group will advocate increased power for parliament and called for direct elections for provincial governors.
Afghanistan's provincial governors are currently appointed by President Hamid Karzai.
The United National Front of Afghanistan includes former mujahedin commanders, members of Afghanistan's communist-era government, and the grandson of former King Zahir Shah.
(with material from dpa)