Kabul, Afghanistan ? After a three-week roller-coaster ride marked by shouting matches, back-door bargaining and boycotts, Afghanistan’s constitutional council broke down again Saturday — this time over a single word.

Leaders called the last-minute hitch shameful, and vowed that today would be the final day for talks on the constitution, which is supposed to help the nation reconcile and rebuild after years of damaging civil war.

The missing word, delegates said, was “official” — the status that speakers of Uzbek and Turkic languages want for their native tongues. The dispute has highlighted Afghanistan’s enduring ethnic divisions.

“Everything is resolved except a difference about one word. Some of the delegates want it and some don’t,” council chairman Sibghatullah Mujaddedi said. “It is shameful we couldn’t bring complete agreement on this word.”

“If we cannot finalize it tomorrow, we will announce to the world that we failed,” he told dismayed delegates seated in a tent on a Kabul college campus.

The ethnic split, led by influential regional leaders, bodes ill for efforts to disarm the unruly militias who control much of the country since helping the United States oust the Taliban two years ago.

The friction pits smaller groups against the Pashtuns, from whom the Taliban drew their strength. It has poisoned the political atmosphere ahead of key national elections slated for the summer.

Foreign officials have warned that Taliban insurgents want to disrupt the convention, and on Saturday night police reported an explosion — possibly a rocket — not far from the meeting site. No damage or injuries were reported.

With U.S.-backed President Hamid Karzai vowing to run only if the constitution installs a dominant chief executive, American and U.N. diplomats have been scrambling to salvage a deal.

Mujaddedi adjourned the meeting to allow more private negotiations.

One prominent delegate said the talks were snagged on whether the language of Uzbek and Turkmen minorities should join Dari and Pashto on the list of official languages.