Poland's new conservative president on Tuesday refused to endorse an amendment to the UN carbon-cutting pact that would require the coal-dependent EU country to further reduce greenhouse gas emissions.

A Brussels-based environmental policy think tank said the decision "stalls the ratification process" on measures to reduce emissions just a month ahead of the landmark UN climate summit in Paris.

But President Andrzej Duda said more analysis of the measure was required.

"Binding Poland to an international agreement affecting the economy and with associated social costs should be preceded by a detailed analysis of the legal and economic impact," he said in a statement.

"These effects have not been sufficiently explained," Duda added, defending his refusal to back the measure.

In line with the United Nations' Kyoto pact, which took effect in 2005, the European Union agreed to slash greenhouse gas emissions by 20 percent by 2020 compared with 1990 levels.

Duda's move came just two days after his conservative allies in the Law and Justice party won parliamentary elections.

The party has vowed to protect Poland's loss-making state-owned coal sector.

The country of 38 million, which is enjoying steady economic growth, gets around 90 percent of its electricity from burning coal.

Experts say Poland's outgoing parliament would need a three-fifths majority to overturn the presidential veto. But few believe parliament will convene to vote on the matter.

The move comes ahead of the November 30-December 11  UN conference in Paris, which aims to seal a landmark climate-rescue deal after more than two decades of fraught negotiations.

"The Polish presidential move stalls the ratification process," Kamila Paquel, a senior analyst with the Brussels-based Institute for European Environmental Policy (IEEP) think-tank, told AFP via email Tuesday.

"The newly elected Polish political leadership has provided a signal that it is not supportive of EU and international climate policy," she added.

"Full ratification would allow the EU's legally binding commitments in the second Kyoto period (2013–20) to enter into force in international law," Paquel said.

Greenpeace Poland said Duda's decision was a "bad sign", saying it could delay the EU's compliance with further emissions reductions or even trigger a "stalemate on decision-making" in the 28-member bloc.