solely on the ground that he or she is one of its nationals, shall, at the request of the State Party seeking extradition, be obliged to submit the case without undue delay to its competent authorities for the purpose of prosecution. Those authorities shall take their decision and conduct their proceedings in the same manner as in the case of any other offence of a grave nature under the domestic law of that State Party. The States Parties concerned shall cooperate with each other, in particular on procedural and evidentiary aspects, to ensure the efficiency of such prosecution. 12. Whenever a State Party is permitted under its domestic law to extradite or otherwise surrender one of its nationals only upon the condition that the person will be returned to that State Party to serve the sentence imposed as a result of the trial or proceedings for which the extradition or surrender of the person was sought and that State Party and the State Party seeking the extradition of the person agree with this option and other terms that they may deem appropriate, such conditional extradition or surrender shall be sufficient to discharge the obligation set forth in paragraph 11 of this article. 13. If extradition, sought for purposes of enforcing a sentence, is refused because the person sought is a national of the requested State Party, the requested State Party shall, if its domestic law so permits and in conformity with the requirements of such law, upon application of the requesting State Party, consider the enforcement of the sentence imposed under the domestic law of the requesting State Party or the remainder thereof. 14. Any person regarding whom proceedings are being carried out in connection with any of the offences to which this article applies shall be guaranteed fair treatment at all stages of the proceedings, including enjoyment of all the rights and guarantees provided by the domestic law of the State Party in the territory of which that person is present. 15. Nothing in this Convention shall be interpreted as imposing an obligation to extradite if the requested State Party has substantial grounds for believing that the request has been made for the purpose of prosecuting or punishing a person on account of that person’s sex, race, religion, nationality, ethnic origin or political opinions or that compliance with the request would cause prejudice to that person’s position for any one of these reasons. 16. States Parties may not refuse a request for extradition on the sole ground that the offence is also considered to involve fiscal matters. 17. Before refusing extradition, the requested State Party shall, where appropriate, consult with the requesting State Party to provide it with ample 32