WASHINGTON (AP) — The United States has withheld $5 million in anti-drug aid to Mexico over concerns about human rights in the country, the State Department said Monday.

It's a small portion of what the U.S. gives Mexico each year but conveys a pointed message to its southern neighbor, which has come under the spotlight for abuses including last year's disappearance of 43 students at the hands of police.

The State Department is obliged by law to hold back 15 percent of some anti-drug aid to Mexico under the Merida Initiative until it delivers a report to Congress on human rights in the country. Spokesman Mark Toner said the department has not sent that report.

"This year the Department was unable to confirm and report to Congress that Mexico fully met all of the criteria in the fiscal year 2014 appropriation legislation, and the 15 percent was redirected away from Mexico," Toner said.

He said that Washington continues to support Mexico's efforts to reform its law enforcement and justice systems, and added that Mexico and the United States "have made significant progress" working to combat organized crime.

In a statement, Mexico's Foreign Relations Department said the country is aware it has challenges and is committed to protecting human rights.

"Nevertheless, it rejects any kind of unilateral practice that judges the human rights situation in a country," the statement said.

Washington sent Mexico $195 million under the Merida Initiative last year, according to State Department figures.

The $5 million in diverted funds will go instead to Peru for efforts to eradicate plantations of coca, the source of the base ingredient for cocaine.

Mexico has been criticized for human rights concerns such as the alleged extrajudicial killings of suspects by security forces and the 2014 disappearance of 43 teachers' college students, who were detained by police in the southern state of Guerrero and have not been heard from since.

Mexican authorities say the students were handed over to a drug gang, killed and incinerated in a garbage dump, though relatives of the victims and international investigators have cast doubt on the official version.

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Orsi reported from Mexico City.