Sens. Amy Klobuchar and Al Franken plan to send a letter to President Obama today with a handful of senators urging the president to renew the administration's efforts to obtain the release of the three American hikers detained in Iran.

Saturday is the one-year anniversary that the hikers, including Minnesotan Shane Bauer, were arrested by Iranian authorities along the border and accused of spying.

Franken and Klobuchar also introduced a resolution in the Senate today with Sens. Robert Casey and Arlen Specter of Pennsylvania and Barbara Boxer of California, calling for Iran "to immediately and unconditionally release" the hikers, Sarah Shourd, Joshua Fattal and Bauer, on humanitarian grounds.

The Obama administration has previously called for the hikers' release, and Secretary of State Hillary Clinton has said the spy charges are "unfounded."

In May, the mothers of the three hikers were allowed to visit their children in Iran, raising hopes that the hikers might be allowed to leave the country.

But no release transpired following the brief visit.