More than 1,000 bone fragments have been found near a lake in Mexico City, authorities and a volunteer group said, just weeks before it hosts the World Cup -- another grim reminder of the country's violent drug war.

A collective of families looking for their loved ones said the gruesome findings near Lake Chalco demonstrated a "devastating reality" and "a forensic crisis of incalculable dimensions."

While "the authorities want this to go unnoticed, the families want the whole world to know the tragedy that occurs in the country's capital," the group said in a statement.

City authorities last week began exhuming the lakefront site in the eastern part of Mexico City, and prosecutors announced Monday that some 300 bone fragments, which they believe could belong to three people, had been found.

But the volunteer group said they found more than 1,000 bone fragments in and around the site, including in areas which had already been examined by government agents.

More than 480,000 people have been killed and another 130,000 have gone missing in Mexico's drug war since 2006, when the government deployed federal troops to take on the country's powerful cartels.

A U.N. committee of experts has called the missing persons crisis a "crime against humanity," saying efforts to recover human remains have been hampered by "acquiescence and omission on the part of public servants."

"International law does not require crimes against humanity to occur nationwide or be orchestrated at the highest levels of government," committee chair Juan Albán-Alencastro said in a statement. "What matters is the scale, the pattern of the attacks, and the targeting of civilians."

Mexican President Claudia Sheinbaum attacked the report, arguing it ignored new policies implemented to support the families of the missing.

In a meeting with city officials on Friday, the activists demanded that searches be carried out without interruption until the site is fully inspected.

Both Mexico City and Guadalajara are preparing to host World Cup games in June, with protesters in both cities denouncing the government's failure to properly investigate the disappearances. The United States and Canada are co-hosting the Cup.

Guadalajara is located in the state of Jalisco, which has more than 15,900 cases of missing persons, a toll that experts attribute to the activities of the Jalisco New Generation Cartel, official data shows. The cartel has been accused of using fake job advertisements to lure new members and of torturing and killing recruits who resist. 

In February, Mexican military forces killed Nemesio "El Mencho" Oseguera, the leader of the Jalisco New Generation Cartel and one of the United States' most-wanted drug lords, leading to an outbreak of violence. After the incident, FIFA reaffirmed its confidence as a host city.

Human remains are routinely found in Jalisco, sometimes in clandestine graves. Earlier this month, the skeletal remains of at least 11 people were found in hidden graves in a rural lot in Ixtlahuacan, a suburb of Guadalajara. Last October, dozens of bags containing human remains were discovered and recovered from a hidden grave near Guadalajara.