San Salvador, El Salvador (CNN) -- Buried underground about 30 miles from El Salvador's capital city, police made a staggering find this week: 213 grenades.
Investigators described the arsenal uncovered Tuesday as "anti-tank grenades" -- the kind of weapons only members of the military are allowed to use in the Central American country.
Key questions remain after the discovery: Who hid the grenades there? And how were they planning to use them?
Authorities say they suspect the stash is yet another sign that Mexico's brutal Zetas cartel has extended its reach. And members of the military could be involved, they said.
"According to our investigations, these have been sold to Zetas drug traffickers in Guatemala and Mexico," Salvadoran Attorney General Luis Martinez told reporters. "And we are going to investigate this. And also we are going to see where they came from."
Authorities have asked the United States for assistance with their investigation into the weapons' origin.
Police said the grenades, buried about 4 feet underground, were manufactured in China and the United States.
CNN's Catherine E. Shoichet contributed to this report.