Philippine President Rodrigo Duterte has accepted China's proposal to jointly investigate allegations that a Chinese fishing vessel abandoned 22 Filipinos after it sank their boat in the South China Sea, his spokesman said on Saturday.

But aside from China and the Philippines, Duterte wants a third country to be included in the joint investigating committee that will be created to determine what really transpired in the Reed Bank, presidential spokesman Salvador Panelo said.

"We are by no means relinquishing any inch of our sovereign rights, nor compromising the rights of our 22 fishermen. We are demanding justice for our countrymen, and we are using all legal means toward that end," Panelo said in a statement.