Heavyweight champion Andy Ruiz Jr vowed to end Anthony Joshua's career in Saudi Arabia after reportedly agreeing to the location for their rematch.

It was announced by Matchroom Boxing earlier in August that British fighter Joshua would look to regain his IBF, WBA and WBO belts from Ruiz in Riyadh on December 7.

However, Mexican-American Ruiz, who caused a huge upset by winning their first encounter in New York with a seventh-round stoppage, initially made it clear publicly he had no intention of defending his titles in the Middle East.

ESPN and The Athletic reported this week that Ruiz had consented to the bout following a number of contractual tweaks, including an increase in his share of the purse.

The reigning champion, who has been tipped to triumph again by WBC heavyweight king Deontay Wilder, appeared to confirm an agreement was reached.

"I dethroned the king June 1st and made history becoming the first Mexican-American heavyweight champion of the world," Ruiz wrote on Twitter.

"I'm looking forward to ending his [Joshua's] career in the desert. I will show the greatness of Mexican boxing in Saudi Arabia."