MEXICO CITY — Honduran election officials said Monday that President Juan Orlando Hernández had won a small majority in a preliminary vote count, but international election monitors backed opposition demands for a partial recount, arguing that there were too many irregularities to be sure of the result.

The political crisis took a new turn late Monday when members of the elite Cobras police unit in Tegucigalpa, the capital, refused to leave their hillside barracks to enforce a 6 p.m. curfew. As night fell, other police units marched into the complex as a growing crowd of bystanders clapped.

“It will be marked down in history that we left, and we left for the reason that we don’t want to violate our own people even more,” said a masked member of the Cobras, who would not give his name or rank.

It was unclear how far the police strike would spread and whether the military would agree to take on the task of patrolling the streets during the curfew.