BUENOS AIRES (Reuters) - Climate change, steel and migration have emerged as sticking points in the final communique that world leaders will issue at the end of the Group of 20 summit in Argentina later this month, an Argentine government official said on Thursday.

FILE PHOTO - Ice on the surface of the southern ocean off the Antarctic coast is seen from the window of a U.S. military plane flying from Christchurch, New Zealand, to McMurdo Station, the biggest U.S. science base in Antarctica, December 7, 2006. REUTERS/Deborah Zabarenko

Those issues were the “most complicated” areas of discussion, said Argentina’s Pedro Villagra Delgado, the lead organizer, or “sherpa,” for the summit of leaders from key industrialized and developing economies.

But he told a press briefing he was optimistic these issues would be resolved in time.

The G20 communique is a non-binding agreement on key international policy issues and will be presented at the conclusion of the two-day summit, which begins on Nov. 30.

Villagra Delgado said the United States was resistant to including language that outlined guidelines for climate goals in the document.

After withdrawing from the Paris Climate Agreement last year, the United States broke with other G20 member countries who have pledged to end coal usage and take steps to reach the goals outlined in the accord.

Villagra Delgado also said China disagreed with the rest of the G20 countries on steel, but did not provide further details over the specifics of their disagreement.

The United States has skirmished with a number of its trading partners - including China - over steel, imposing a 25 percent duty on imports of steel and a tariff of 10 percent on aluminum.

Other countries objected to including language about immigration in the communique, Villagra Delgado said, but would not elaborate on which countries expressed concern.

Reform of the World Trade Organization (WTO) may also be a topic of discussion at this month’s meeting, Villagra Delgado said, but added that specific issues to be discussed in the G20 sessions were still being worked out.

U.S. President Donald Trump has threatened to pull out of the WTO, while China has claimed the 20-year-old organization’s dispute resolution mechanisms are outdated in the current global economy.