Except as specifically provided in any agreement for cooperation, no source or special nuclear material hereafter exported from the United States may be enriched after export without the prior approval of the United States for such enrichment: Provided, That the procedures governing such approvals shall be identical to those set forth for the approval of proposed subsequent arrangements under section 2160 of this title, and any commitments from the recipient which the Secretary of Energy and the Secretary of State deem necessary to ensure that such approval will be obtained prior to such enrichment shall be obtained prior to the submission of the executive branch judgment regarding the export in question and shall be set forth in such submission: And provided further, That no source or special nuclear material shall be exported for the purpose of enrichment or reactor fueling to any nation or group of nations which has, after March 10, 1978, entered into a new or amended agreement for cooperation with the United States, except pursuant to such agreement.