Eto’o, record four-time winner of the African Footballer of the Year award, broke the news after a 1-0 win over Libya at the weekend.
A Cameroon football official said in Yaounde that Eto’o, 32, announced his retirement to team-mates in the dressing-room after the match.
“He did not give reasons why he is retiring from the national team,” said the official, speaking on condition of anonymity.
“Samuel thanked his team-mates for all the efforts they have made to allow him to become a better player. They prayed together and he left.”
An Eto’o corner led to Aurelien Chedjou heading the winner and enabling Cameroon to top Group I after struggling for much of the campaign.
The recent Chelsea recruit from Russian club Anzhi Makhachkala limped off injured on the hour mark.
A draw in Cairo on September 16 will reveal who six-time World Cup qualifiers Cameroon face over two legs for a place at the 2014 finals in Brazil.
Possible opponents include top-five ranked countries Ivory Coast, Ghana, Algeria and African champions Nigeria.
Eto’o has regularly disagreed with Cameroon coaches and his retirement may be linked to the selections of incumbent Volker Finke.
The German reportedly ignored calls from Eto’o to start with goalkeeper Carlos Kameni and striker Achille Webo against the Libyans.
Eto’o was banned from the ‘Indomitable Lions’ last year after inciting a bonus-related boycott of a friendly in Algeria.
Recalled for a Cup of Nations qualifier against Cape Verde, he could not prevent Cameroon missing the 2013 finals in South Africa.
Born in Atlantic city Douala, the 1.80m star played for Real Madrid, Mallorca, Barcelona and Inter Milan before joining big-spending Anzhi.