Hailu Shawl, who heads the All Ethiopians Unity Party, says his observers were beaten and driven away from polling stations across the country, Radio France Internationale reported Wednesday.
Provisional results indicate Mele Zenawi's Ethiopian People's Revolutionary Democratic Front won 499 of 536 seats.
"Look at the results," Hailu says. "They don't look real."
Hailu says a court challenge is one possibility his party is considering.
David Shinn, the former U.S. ambassador to Addis Ababa, says the European Union will probably accept the election results.