PARIS (REUTERS) - French Prime Minister Edouard Philippe on Wednesday (Dec 20) defended the cost of a recent overseas trip to New Caledonia and Japan, following criticism in the country's media of the expenses incurred and the use of a private plane.

The criticism followed similar rebukes this month of President Emmanuel Macron's 40th birthday celebrations in the grounds of a royal palace, which Macron's office sought to play down, saying the event had been paid for by Macron and his wife.

Philippe and the French delegation took a private plane to fly from Tokyo to Paris on their way back from an official trip to New Caledonia earlier this month at a cost of 350,000 euros (S$560,000).

"I totally understand the surprise and the questions of the French people," Philippe told RTL radio.

"We knew there was no commercial flight (from Tokyo) at the time we needed to return, and we knew we had to return because the President was leaving on the Wednesday morning of our return for Algeria," he said.

"The rule is that, whenever possible, the Prime Minister or the President must be on the national territory... I take full responsibility for this decision," added Philippe.

President Emmanuel Macron put financial and ethical probity in public life at the heart of his presidential campaign and his new government passed a law earlier this year to tighten up on ethical standards in French politics.

However, some of Macron's political opponents have branded the former investment banker as a "president of the rich" due to policies such as the scrapping of a wealth tax and cutting housing benefit - moves which the president has framed as reforms to boost investment and social mobility.