Bongo's camp said on Sunday that it was set to win the single-round contest and accused Ping's supporters of fraud, charges that could presage confrontation between the two sides.
The Central African oil producer's interior minister called Ping's move to pre-empt an official announcement of the poll results, which is expected on Tuesday, by declaring victory an attempt to manipulate the democratic process.
"Based on nearly all the affidavits ... we are able to affirm that I am the winner of the presidential vote," Ping said. "I encourage Ali Bongo to submit to the verdict of the ballot box."
He also called upon the Gabonese people to "defend their choice throughout the country and overseas".
Ping said he had told the American and French ambassadors in Libreville that he intended to guarantee the security of Bongo and his family, who have ruled the nation of some two million people for nearly 50 years.
Bongo, 57, first won election after his father Omar died in 2009 after 42 years in office. Declining oil output and falling prices have resulted in budget cuts in recent years, however, providing fodder for opposition claims that average Gabonese have struggled under his leadership.
--reuters--