The suspect in a machete attack on two churches in southern Spain in which one clergyman was killed and another seriously injured was due to be deported, police have said.

The 25-year-old is Moroccan and was arrested after a man wielding a machete attacked several people at the churches of San Isidro and Nuestra Senora de La Palma, around 300 meters apart, in the southern port city of Algeciras.

Police said they took the suspect to his home overnight for detectives to conduct a search, a spokesman for Spain's National Police said.

He is expected to be transferred to the Spanish capital Madrid to appear before a High Court judge on terrorism charges.

A police source denied local media reports that the suspect had been under surveillance by security operatives in the days or months before the attack.

READ MORE

Why does Ukraine want Western tanks?

Bosnia's river of rubbish

The Secret Betrayal: China's WWII sailors

He had no criminal nor terrorism-related convictions either in Spain or other allied countries, according to the source.

The man was not in Spain legally and his deportation process began in June last year and was ongoing, the source added.

Diego Valencia, a sacristan at the Nuestra Senora de La Palma church, was killed after the assailant chased him out of the church and attacked him in the busy square outside, police and church groups said.

A second man, the priest of the parish church of San Isidro, Antonio Rodriguez, was operated on for serious knife wounds and is said to be in a stable condition.

Local media said three others were injured, though police did not confirm.

An official day of mourning has been declared by the city's mayor who will host a gathering on Thursday outside the church where Valencia died.

Spain's Interior Minister Fernando Grande-Marlaska, who will travel to the city on Thursday, said the search of the suspect's home will help police determine if terrorism was at play.

"There were no third persons involved in what happened," he said.

Mayor José Antonio Landaluce has also asked the Interior Ministry for an increase in security for the city.

The port of Algeciras in the Andalucia region serves as the main entry point for Moroccans arriving in Spain.

Spain suffered the worst Islamist militant attack on record in Europe in 2004, when 192 people were killed and more than 1,800 injured in multiple bombings on Madrid's train system.

In 2017, 16 people were killed and nearly 200 injured in a series of attacks that included Islamist militants in a van mowing down pedestrians on Barcelona's Las Ramblas boulevard.