MANILA (Reuters) - The vice president of the Philippines on Thursday rebuked the country's leader for being "reckless" in suggesting he would consider ignoring an arbitration ruling in its favor over a territorial dispute with China in order to forge a joint energy deal with Beijing.

Leni Robredo, who also leads the opposition, described as "extremely irresponsible" President Rodrigo Duterte's apparent openness to concede to China and accept its offer to jointly develop gas reserves, which an international tribunal ruled Manila had the right to exploit.

Entering into any deal should not come at the expense of upholding the country's rights in the South China Sea, Robredo said in a statement.

Robredo was elected separately to Duterte and was not his running mate. She has a frosty relationship with the president, who often mocks her during his public speeches.

Duterte on Tuesday said Chinese President Xi Jinping told him that Beijing was ready to be a minority partner in a joint energy venture at the Reed Bank, but the Philippines must first set aside the 2016 award by the Permanent Court of Arbitration in the Hague, a ruling China does not recognize. [nL3N2621VE]

Its interpretation of maritime boundaries also ruled that China's claim to most of the South China Sea had no legal basis under United Nations maritime law, in what was a big blow to Beijing.

Robredo said Duterte's remarks were "profoundly disappointing" and said the Philippine constitution already allowed partnerships with foreign firms within the country's Exclusive Economic Zone (EEZ), without the need to make concessions.

The arbitral ruling is still subject to talks between the two countries, presidential spokesman Salvador Panelo told a regular news conference. Meanwhile, the countries could focus on items that could be of mutual benefit, he added.

Since taking office in 2016, Duterte has pursued warmer ties with China, avoiding criticism or confrontation with Beijing exchange for billions of dollars in loans, grants and investment, much of which have yet to arrive.

Former Foreign Secretary Albert Del Rosario, who was among those who sought arbitration, said Duterte did not need to give anything away.

"To come up with an economic activity in our EEZ need not involve setting aside the arbitral ruling and running afoul of the constitution," del Rosario said.

(Reporting by Neil Jerome Morales; Editing by Martin Petty and Alex Richardson)