More than a million people in Mexico are descended from African slaves and identify as "black", "dark" or "Afro-Mexican" even if they don't look black. But beyond the southern state of Oaxaca they are little-known and the community's leaders are now warning of possible radical steps to achieve official recognition.

"The police made me sing the national anthem three times, because they wouldn't believe I was Mexican," says Chogo el Bandeno, a black Mexican singer-songwriter.

"I had to list the governors of five states too."

He was visiting the capital, Mexico City, hundreds of miles from his home in southern Mexico, when the police stopped him on suspicion of being an illegal immigrant.

Fortunately his rendition of the anthem and his knowledge of political leaders convinced the police to leave him alone, but other Afro-Mexicans have not been so fortunate.

Image caption Chogo el Bandeno (right) with visiting Malian musician Lassana Diabate

Clemente Jesus Lopez, who runs the government office in charge of Afro-Mexicans in Oaxaca state, recalls two separate cases, both involving women.

"One was deported to Honduras and the other to Haiti because the police insisted that in Mexico there are no black people. Despite having Mexican ID, they were deported."

With the help of the Mexican consulates they were able to return but were offered no apology or compensation, Lopez says.

Black Mexicans have been living in the Costa Chica area, on the Pacific coast of Oaxaca, since their ancestors were brought from Africa as slaves in the 16th Century.

Colonial Spanish cattle ranchers often used them as foremen, in charge of indigenous Mexican workers who were not used to animals the size of cows or horses.

Image caption Black cowboy, Antonio Prudente Lopez, says about 10% of Santiago Llano Grande share his profession

But outside the Costa Chica area there is little awareness of their existence.

An interim census in 2015 indicated a black population of 1.4 million, or 1.2% of the Mexican population. Even in Oaxaca state they only account for 5% of the total.

You may have had a grandmother who was black and feel black, even if you don't look it Tulia Serrano Arellanes

By comparison, indigenous peoples made up nearly 10% of Mexico's population, as measured in the 2010 census.

The appearance of those who identify as black Mexicans varies considerably. Some are hard to distinguish from indigenous Mexicans.

"It's not only about skin colour, it's also about how you feel," says Tulia Serrano Arellanes, a council worker. "You may have had a grandmother who was black and feel black, even if you don't look it."

Much of their identity is based on where they live - if you live in a black town such as Santiago Llano Grande, as Chogo el Bandeno does, you are likely to think of yourself as black.

But there is also a common culture.

For example, there's a distinctive style of music called the chilena, which was brought to the Costa Chica in the 19th Century by Chilean sailors on their way to the gold rush in California, which black musicians have adapted.

They have added Afro-Mexican instruments such as the quijada, a dried out donkey's jawbone with rattling molar teeth. There's also the bote, a friction drum - you rub a stick attached to the drum skin and it makes a kind of growling percussive noise. These sounds are a central part of Afro-Mexican musical life.

There are also dances that hark back to the colonial ranching days, including the Dance of the Devils, performed around the Day of the Dead at the end of October and in early November.

The dancers wear "devil" masks, and are led by the brash character "Pancho", who plays the colonial ranch foreman.

He struts around with a whip while his buxom "white" wife - played by a black man - flirts outrageously with the "devils" and even with the audience.

In the towns of the Costa Chica, even nursery-age children learn steps of the dance and are taught to take pride in their black heritage.

But there is frustration here that the Afro-Mexicans are not more widely known in Mexico and are not officially recognised as a minority by the Mexican government.

According to Humberto Hebert Silva Silva, head of the Bureau for Afro-Mexican Affairs in Oaxaca, this is because Afro-Mexicans speak Spanish, like most other Mexicans - they do not have their own language.

"When we go and ask [for recognition as a minority], they come up with excuses, or say that we don't have an indigenous mother tongue. Language is the real criterion," he says. "We are being discriminated against."

If Afro-Mexicans were classified as a minority they would receive extra funding for promotion of their culture and public health programmes.

But activists including Israel Reyes, a teacher, want more than money, it's also important to them that the existence of Afro-Mexicans is recognised at the level of the Mexican state.

"The story of the black population has been ignored and erased from history," he says.

The activists' efforts have born some fruit.

The 2015 interim census for the first time gave respondents the option to identify themselves as black - negro in Spanish - though this is not a term used by all Afro-Mexicans, many of whom call themselves "dark" (moreno) or use other, local terms to describe themselves.

It can't be right that the constitution of our country doesn't recognise us Humberto Hebert Silva Silva

But some Afro-Mexicans are impatient for more recognition.

Humberto Hebert Silva Silva warns that the black community may end up emulating the indigenous uprising in Chiapas in the 1990s, known as the Zapatistas.

"So far the black communities have endured discrimination and they have stuck to legal avenues, which they have now exhausted," he says.

"With the Zapatistas, the indigenous rose up, and it was an armed uprising, to claim their rights. And well, our community is thinking the same. It's thinking, in the distant future, to rise up too," he says.

"It may be the only way to get the rights we're entitled to. It can't be right that the constitution of our country doesn't recognise us. There's a big gap between what the politicians say and what they do. We'll have to take action to give them a warning."

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The Afro-Mexicans is broadcast on the BBC World Service from 04:00 GMT on Sunday 10 April - catch up on BBC iPlayer Radio

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