SAN SALVADOR, Sept 16 (Reuters) - El Salvador"s vice president has delivered the final proposal for constitutional changes to President Nayib Bukele, including the extension of presidential terms and a new electoral tribunal body, the government said on Thursday. The president"s legal adviser, Javier Argueta, said in an interview with a local television station that Bukele will review and study the proposals before sending them to Congress, where Bukele"s party has a large majority. A team of lawyers led by Vice President Felix Ulloa had been drawing up the controversial proposals that have worried rights groups and U.S. officials, who are concerned about what they see as democratic backsliding and authoritarianism under Bukele. The lawyers put forward 216 reform proposals to the constitution relating to fundamental rights as well as El Salvador"s political and economic system. "El Salvador is in a foundational phase. We are founding a new country and with that new vision of the future we have collected this document from the people," Ulloa said in a video released by the government at midnight on Wednesday. At the moment, the reform package would need be approved in one legislature and ratified by the other, before it could take effect. Bukele"s government, however, proposes bypassing Congress and ratifying the changes to the Constitution through a referendum. Bukele would be in a strong position to push through any changes via a referendum due to his high approval rating, which stands close to 85%, according to a recent poll by the newspaper La Prensa Grafica. The changes which have generated criticism from pro-democracy activists include a suggestion to extend the presidential term from five to six years starting in 2029. The proposals also include mechanisms for citizen participation such as referendums and plebiscites, as well as the creation of a constitutional court and a new national electoral institute. Bukele has pushed back against accusations of authoritarianism, arguing he is cleaning up the country.