BRUSSELS (Reuters) - The number of African migrants arriving in Italy after crossing the Mediterranean from Libya dropped by more than half in July from June, the European Union’s border agency Frontex said on Monday.

Migrants sit on the ground after disembarking from Vos Hestia ship of NGO "Save the Children" in the Sicilian harbour of Augusta, Italy August 4, 2017. REUTERS/Antonio Parrinello

But the number of migrants on a secondary, western Mediterranean route to Spain rose sharply last month, it said.

Frontex said 10,160 migrants arrived from Northern Africa on Italy’s southern shores in July, 57 percent fewer than in June and the lowest level of arrivals in July since 2014.

Bad weather and clashes in the region of Libya from where many migrants depart on smugglers’ boats contributed to the decline, the agency said.

“In addition, increased presence of the Libyan Coast Guard also discouraged the people smugglers from sending out boats with migrants,” Frontex said.

Italy has been the main gateway to Europe since a 2016 deal with Ankara shut off the route from Turkey to EU member Greece, which had mostly been used by Syrian refugees.

Frontex said 2,300 migrants made it to Spain in July, more than four times as many as a year earlier. Arrivals in Spain in the first seven months were “around 11,000, already exceeding the number for all of 2016,” it said.

Both the western route leading to Spain and the central Mediterranean one to Italy carry African nationals. The EU considers most of them to be labor migrants - rather than refugees - and does not want to take them in.

Immigration is dominating Italy’s political agenda before elections early next year, with public opinion increasingly hostile to migrants. Almost 600,000 migrants have arrived in Italy over the past four years.

The EU has been increasingly engaging in Libya to prevent departures, despite heavy criticism from rights groups that the policy fails to help those in need as required by international law.