The US definitely should tell them that all Iranian visas are on hold pending the release of the British soldiers, and on hearing what they have to say.
There is a problem with that......
As the host country of the U.N., we are bound by law to expedite visas for any member, even if we were at war with them, which is not yet the case but could be.
It is one of the problems a host country faces when we are forced to separate politics and war from the U.N. member states.