Recruiters typically seek out the highest-qualified applicants for executive-level positions. If they say you're underqualified, they might just mean that you're underqualified for the positions they're currently looking to fill. However, it might also be that they don't understand your qualifications or credentials. Find degrees equivalent to your own in the US that you can use for comparison. You might also check to see if your field requires specific licenses or certifications in the US that you don't have.