Costa Rican opposition parties denounced the decision of the Legislative Assembly, describing it as "illegal" and "in violation of national sovereignty," Presna Latina reported Saturday.

The decision grants US troops permission to stay in Costa Rica from July 1 to December 31 to fight drug trafficking.

http://www.presstv.ir/detail.aspx?id=133377§ionid=351020706
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UPDATE #1
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Costa Ricans suspect 'ulterior motive' in permitting large numbers of US troops

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Opposition leaders in Costa Rica are up in arms over an agreement between the country and the United States that reportedly allows 46 US warships and 7,000 US Marines to enter the country as part of an anti-drug effort.
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According to several Costa Rican news sources, the government there signed an agreement with the US last week to extend an 11-year-old cooperative program aimed at eradicating the maritime drug trade.