Why does Imam Khamenei say the US offer to help Iran fight the coronavirus is strange?

The Americans have said they are willing to help us in terms of medication and in treating the Coronavirus. This is very strange. First of all, according to what your own officials have said, you have shortages of medication. If you have some, use it for your own patients. Secondly, you are accused of having created this virus. I do not know how accurate this assertion is. But, with the existence of such an accusation, which sane person can trust you?

Imam Khamenei, Mar 22, 2020