KATOWICE, Poland — Efforts to agree on the fine print of the Paris climate accord drew closer Thursday, three years after the landmark agreement on curbing global warming, but negotiators remained deadlocked on the thorniest issues and appeared set for overtime.

A summary text from the Polish diplomat chairing the talks was expected around midnight as the two-week U.N. climate summit in the southern Polish city of Katowice neared its scheduled end on Friday.

Diplomats and ministers had huddled behind closed doors, some overnight, weighing every word of the draft text covering issues such as how countries will count both their greenhouse gas emissions and their efforts to reduce them.

Along with the Paris accord rulebook, the other main issues at the talks are how much financial support poor countries will get to combat and adapt to climate change, and what kind of message to send about future work to curb climate change.

Last week, the United States, Russia, Saudi Arabia and Kuwait blocked the endorsement of a scientific report on a key element of the Paris climate agreement: capping global warming at 1.5 degrees Celsius (2.7 degrees Fahrenheit), if possible. That angered other countries and environmentalists, who accused the four oil-exporting nations of stalling progress toward the accord’s most ambitious emissions-cutting target.