Five severed heads are placed in a sack and left on a suburban street in Acapulco, Mexico, on September 27, 2011.

Story highlights

NEW: A message left by a drug gang claims responsibility, the city's prosecutor says

NEW: Mexico's defense ministry is near the site where the heads were found

The heads were found near the border between Mexico City and neighboring Mexico state

Brutal turf battles between drug cartels, common elsewhere in Mexico, are rare in the capital

Mexico City CNN  — 

Authorities found two severed heads along a highway in Mexico City on Monday morning, the city’s attorney general said.

The heads were inside a car near the border dividing the city from neighboring Mexico state, Attorney General Miguel Mancera told reporters. The nation’s defense ministry was also nearby.

A lengthy message was left beside the heads, Mancera said, detailing that a drug gang known as “The Hand With Eyes” was responsible.

“It ends saying that the territory of ‘The Hand With Eyes’ is so extensive that it has reached the metropolitan area and hasn’t disappeared,” Mancera said.

Police in Mexico City arrested the gang’s suspected leader, Oscar Osvaldo Garcia, also known as “The Hand With Eyes,” in August.

Mancera said Monday that authorities remained committed to tracking down members of the gang and stopping its growth.

Authorities were still working Monday to identify the victims.

Beheadings have become a signature sign of the brutally violent turf battles between drug cartels that have plagued cities across Mexico.

Last week authorities in the beach resort city of Acapulco made a similar discovery, finding five severed human heads inside a small wooden crate, Guerrero state authorities said.

But such violence is rare in the country’s capital.

“Mexico City has been surprisingly calm in the midst of the turbulence of this conflict with organized crime, while other major cities are experiencing major upturns in violence,” said Eric Olson, a security expert at the Mexico Institute of the Woodrow Wilson International Center for Scholars in Washington. “It hasn’t exploded the way it has (elsewhere). There’s always that fear of that happening, because there’s nothing to guarantee that it won’t.”

CNN’s Krupskaia Alis, Rene Hernandez, Rafael Romo and Catherine E. Shoichet, and contributed to this report.