NICOSIA, Cyprus—Cyprus has asked its European partners to help ease a cash crunch at the island's biggest lender, saying this spring's bank-rescue deal was struck "without careful preparation" and was imperiling its ability to meet budget targets.

In a letter sent to European leaders, Cyprus President Nicos Anastasiades said the success of the island's bailout depended on Bank of Cyprus PCL's survival, and he criticized capital controls put in place as part of the deal, which he said are severely damaging the economy.

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