Opposition candidates Monday accused election officials of fraud and voting irregularities after Sunday’s presidential election in Cameroon.

The charges came from at least three candidates who campaigned against President Paul Biya, including the main opposition candidate John Fru Ndi of the Social Democratic Front, who said fake indelible ink used for marking voters’ fingers was distributed to polling stations. Similar charges came from Jean Jacque Ekindi and Dr. George Nyamndi Dobgima.

Complaints also came from voters.

Valokossa Mohamadou, 29, showed CNN how he was able to remove ink from his thumb using saliva, minutes after voting in Yaounde, the capital. Easily removable ink opens up the possibility of people voting multiple times in the West African nation.

Ndula Bertin said her name was missing from the list at a polling station.

Efforts to reach election officials by CNN about the charges were not immediately successful.

Cameroonians went to the polls Sunday amid relative peace and calm nationwide. There were threats of violence ahead of the vote.

Biya, 78, who has been in power for nearly 30 years, cast his ballot under heavy security. He is seeking another seven years in office.

Election officials have up to 15 days to announce election results, but cabinet minister Laurent Esso predicted a landslide victory for Biya shortly after he cast his ballot Sunday.

In 2007, Biya won 70 percent of the vote in a race against Ndi.