Mexico City - A Mexican archaeologist said his team has found a tunnel-like passageway that apparently leads to two sealed chambers, the latest chapter in the search for the as-yet undiscovered tomb of an Aztec ruler.

The Aztecs are believed to have cremated the remains of their leaders during their 1325-1521 rule, but the final resting place of the cremains has never been found. Outside experts said on Tuesday that the find at Mexico City's Templo Mayor ruin complex would be significant.

The National Institute of Anthropology and History said Monday that a team led by archaeologist Leonardo Lopez Lujan had discovered an 8.4-mt (27-ft) long tunnel leading into the center of a circular platform where dead rulers were believed to be cremated.

The mouth of the tunnel was sealed by a 3-ton slab of rock. When experts lifted it in 2013, they found a hollow space marked by offerings by both rich and grisly.

Gold ornaments and the bones of eagles and infants were found in an offering box. Two skulls of children between five and seven years old were found with the first three vertebrae, suggesting they may have been decapitated. The kind of stone knives used in human sacrifices were also found, as well as a hand and bones from two feet.

But one researcher detected signs that a passageway appeared to lead deeper into the ceremonial platform, known as the Cuauhxicalco (kwow-she-KAL-koh), where written accounts from after the 1521 Spanish conquest indicated that rulers' remains were burned.

The passageway proved to be about 18 inches (45 centimeters) wide and 5 feet (1.5 meters) high.

"Once the rocks and dirt were dug out, we saw that it led directly into the heart of the Cuauhxicalco," Lopez Lujan said. "At the end (of the passageway), there are what appear to be two old entrances that had been sealed up with masonry."

It would be a logical place for rulers remains to lie - the Templo Mayor site was the most significant temple complex in the Aztec capital, known as Tenochtitlan - but Mexican archaeologists have been searching in vain for the tombs for years.