By Marcelo Rochabrun and Marco Aquino LIMA (Reuters) - The leader of the socialist party that appears poised to win Peru's presidential election claimed victory on Friday with its candidate Pedro Castillo holding a razor-thin over right-wing Keiko Fujimori. With more than 99.5% of votes tallied and only a handful of contested ballots to be added, Castillo had 50.2% of the vote, around 60,000 votes ahead of Fujimori who has pushed allegations of fraud, though with little proof. The country's electoral authority has yet to confirm the win, but most observers and some regional leftist leaders including from Argentina and Bolivia and have proclaimed Castillo as the victor. Several presidents in the world are congratulating the victory of Pedro Castillo, in other words, he has solid international legitimacy, wrote Vladimir Cerron, the leader of the Free Peru party, on Twitter. Cerron, a Cuba-trained surgeon and Marxist-Leninist, is a former regional governor who could not run for president himself as he has been sentenced on corruption grounds in the past. Fujimori has yet to concede the election with fewer than 100,000 votes remaining and her supporters have called for protests against the result. The daughter of jailed former President Alberto Fujimori, she has doubled down on unsubstantiated allegations of fraud, and members of her party have said they will not concede until all votes and appeals are counted, which could still take days. Castillo himself has also stopped short of proclaiming himself the winner, although he did say earlier this week that the party had assured him he would be the winner. The election has bitterly divided Peruvians, with higher-income citizens supporting Fujimori while low-income ones supported Castillo. Castillo, an elementary school teacher and the son of impoverished peasant farmers, has galvanized rural support in Peru. He was not a member of the Free Peru party before his presidency run. It is still unclear whether he would adopt a far-leftist stance for the economy if in power. In recent days, he has recruited Pedro Francke, a moderate left economist as his adviser, who has looked to foster a more market-friendly tone. (Reporting by Marcelo Rochabrun and Marco Aquino; Editing by Alistair Bell)