Michael Williams, U.N. special envoy for Lebanon, and Angelina Eichhorst, the European Union's head of delegation, issued an appeal for the Estonian cyclists.
"The bicyclists came to Lebanon as tourists, with no ill intent," Williams and Eichhorst said in a statement. "This criminal act is a reminder of a dark part of Lebanon's history, which could threaten Lebanon's standing in the international community."
Seven Estonian cyclists were kidnapped by gunmen in late March after crossing the Syrian border with Lebanon.
A previously unknown group calling itself the Renaissance and Reform Movement issued an e-mail statement to Lebanese media demanding an unspecified ransom and Lebanese authorities had expressed concern that Syria might be behind the abductions.
Lebanese authorities said they had several suspects in custody in connection with the abductions. The ransom note added the Estonians were in good condition but declined to indicate where they were held.