MEXICO CITY (Reuters) - Mexican authorities raised the alert level for the Popocatepetl volcano on Saturday after an increased level of explosive activity belched ash over Mexico City and pushed international airlines to suspend flights.

The alert level for the towering Popocatepetl volcano, located some 50 miles to the southeast of the capital, was raised to yellow phase three from yellow phase two, Mexico's National Center for Disaster Prevention said in a statement.

It is the third-highest warning on the center's seven-step scale.

Luis Puente, head of Mexico's civil protection office, said via his Twitter account that authorities were making sure evacuation routes for nearby communities were clear, but that flights out of Mexico City would continue.

Still, some international airlines canceled flights in recent days as a fine ash fell over the capital and surrounding towns. Mexican authorities have insisted the level of ash in the air does not pose a risk for planes.

The change in activity in the 5,450-meter (17,900-foot) volcano could provoke big explosions capable of sending incandescent fragments out over considerable distances, the center added.

Authorities had raised the alert level last May, but dropped it back down to yellow phase two in June.

(Reporting by Michael O'Boyle; Editing by Sandra Maler)