Eligibility for award of contracts under this chapter or of any other contract by the Secretary of State, including lease-back or other agreements, the purpose of which is to obtain the construction, alteration, or repair of buildings and grounds abroad, when estimated to exceed $5,000,000, including any contract alternatives or options, shall be limited, after a determination that adequate competition will be obtained thereby, to (1) American-owned bidders and (2) bidders from countries which permit or agree to permit substantially equal access to American bidders for comparable diplomatic and consular building projects, except that participation may be permitted by or limited to host-country bidders where required by international agreement or by the law of the host country or where determined by the Secretary of State to be necessary in the interest of bilateral relations or necessary to carry out the construction project.