MEXICO CITY (AP) — Heavily armed gunmen attacked and wounded Mexico City’s police chief in a brazen operation that left an unspecified number of dead, Mayor Claudia Sheinbaum said Friday.

Sheinbaum said on Twitter that Security Secretary Omar García Harfuch was being treated in a hospital, but was out of danger. “There were deaths and several arrests,” she said.

Sheinbaum said she would share more information at a news conference later in the day.

Mexico City Attorney General Ernestina Godoy Ramos said onTwitter that there were 12 arrests and that her office was investigating the attack.

The police said in a statement that gunmen armed with .50 caliber sniper rifles and grenades exchanged fire with the chief's security detail. The statement said two police were wounded. Harfuch was hospitalized in stable condition, it said.

The attack occurred around 6:30 a.m. on Mexico City's grand boulevard Paseo de la Reforma in an area of large homes surrounded by walls and foreign embassies. Photographs from the scene showed a bullet-riddled black SUV and a high-sided construction truck with a number of rifles in the back that apparently hid the gunmen until the ambush.

There was no immediate word on motive or the identity of the attackers, but a number of organized crime groups operate in the city.

President Andrés Manuel López Obrador offered his support and solidarity to Sheinbaum and the city's public security forces.

“It has to do without a doubt with the work he is carrying out to guarantee peace and tranquility,” López Obrador said.

Mexico's federal Security Secretary Alfonso Durazo, who was travelling with the president, condemned what he called a “cowardly” attack. “It's clear that the work of the (police) is touching strong criminal interests,” he tweeted.

Earlier this month, a federal judge and his wife were killed at their home by gunmen in the western state of Colima. The judge had handled a number of cases related to organized crime.