LIMA (Reuters) - Peru's congress gave President Pedro Castillo the go-ahead on Thursday to attend this month's Summit of Americas, adding another South American president to a meeting that the United States is hosting but that has seen uncertainty over attendance.

       The legislature's approval is a requirement in Peru for presidents to take international trips. Castillo received a formal invitation in May from U.S. President Joe Biden to attend the gathering in Los Angeles.

       The summit aims to improve cooperation in the region, but there has been last-minute uncertainty around the final guest list. Invitations have been slow to roll out from Washington amid protests from regional leaders over the host nation's exclusion of the leaders of Venezuela and Cuba.

       On Wednesday, Argentina's President Alberto Fernandez confirmed his presence at the meeting. Brazil's leader Jair Bolsonaro and Chile's Gabriel Boric are also expected to attend.

       (Reporting by Marco Aquino; Writing by Carolina Pulice and Brendan O'Boyle; Editing by Frances Kerry)