Costa Rica has granted the U.S. military a six-month window to bring 7,000 Marines, five planes and 46 warships into its territory to help stem the flow of drugs northward.

The Central American country has increasingly become a target for drug traffickers as intelligence and law enforcement agencies have cut off other routes through Mexico. Without an army and with long coastlines and poorly guarded borders, Costa Rica is vulnerable to drug cartels using well-refined transportation mechanisms and the latest technological equipment, security experts say.

Some Costa Rican legislators voiced concern about the authorization, saying it gives the United States a “blank check” to use its territory and threatens the nation's sovereignty.

According to a letter from Costa Rican Public Security Minister José María Tijerino, specific requests to dock or unload U.S. military ships must be submitted to the country one month in advance.

The permission was granted by a 31-8 vote of the Legislative Assembly on Thursday night and allows the United States to use the country's territory through Dec. 31.