FREETOWN (Reuters) -Sierra Leone President Julius Maada Bio secured victory in the West African country's presidential election with more than 56% of the votes to avoid a run-off against main rival Samura Kamara, the electoral commission said on Tuesday.

Bio, 59, was running for re-election after a first term marred by growing frustration over economic hardship.

"I hereby certify that Bio Julius Maada having polled... 56.17% of the total valid vote cast ... is elected president," Sierra Leone's chief electoral commissioner Mohamed Kenewui Konneh said.

Kamara, 72, who suffered a narrow defeat in the 2018 election, received about 41% of the votes this time.

"These results are not credible and I categorically reject the outcome so announced by the electoral commission," Kamara said on Twitter after the announcement of final results.

The election has been tense, with violence breaking out before, during and after the vote.

There were fears as results were announced that more unrest could occur if none of the 13 candidates secured the 55% of votes required to avoid a runoff.

Kamara's camp has already rejected partial results showing Bio in the lead, citing irregularities and lack of transparency.

International observers and the United States have also voiced concern about a lack of transparency in the counting process.

Any citizen who lawfully voted may submit challenges to the Supreme Court of Sierra Leone within seven days of the election results being declared, Konneh said.

Bio addressed the nation after the publication of provisional results on Monday evening and called on citizens to remain peaceful.

(Reporting by Cooper Inveen, Bate Felix and Umaru Fofana;Writing by Anait Miridzhanian and Sofia Christensen;Editing by Alison Williams, David Goodman and Grant McCool)