Barcelona airport security staff on Monday intensified their strike action, just as the summer holiday season entered its busiest period.

Spain's Civil Guard was forced to step in as officials scrambled to guarantee the necessary security checks at the country's second-largest airport.

Spain's public works minister, Inigo de la Serna, said that the Civil Guard's presence at El Prat, Spain's second largest airport, would ensure a return to normality after weeks of flight delays. He added that it was imperative to guarantee a high degree of airport security, with Spain on high alert in case of a terror attack.

The Civil Guard is a national police force with an organizational structure similar to that of the military and is comparable to the French Gendarmerie and the Italian Carabinieri.

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Initial reports suggested that waiting times at security checks were less than 30 minutes on Monday morning, indicating that the government was fulfilling its promise to provide up to 90 percent of the regular service during the strike.

In recent weeks, waiting times at El Prat have exceeded several hours, as airport security staff have staged a series of partial walk outs in a dispute over pay and working conditions.

Employee representatives at private security firm Eulen, which employs some 86,000 security staff in 14 countries, rejected a pay-rise offer of 18 percent ahead of the strike.

Barcelona has seen a sharp spike in the number of tourists visiting the city, with airport passenger numbers increasing by around 60 percent between 2009 and 2016. However, according to striking airport staff, security personnel numbers at El Prat have decreased in that same period, from 500 to 360.

dm/kms (dpa, AFP, AP)