Speaking in the Egyptian capital Cairo, Ahmed Al-Tayeb called on Libyan officials and soldiers to "refuse to obey orders given to them by the regime to shed Libyan blood."
Otherwise, he said, they would be "accomplices in the offense."
He also appealed to Arabs and people worldwide to support Libyans by providing humanitarian and medical support.
Libyans have been calling on citizens of neighbouring countries to pass medical supplies and cell phones through the borders, after violent clashes between pro-democracy protesters and security forces loyal to leader Moamer Gaddafi left hundreds killed.
The United Nations estimates the number of deaths at 1,000.
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