As per IRS website "To be a qualifying child for the child tax credit, the child must be a citizen, national or resident of the United States and must not have attained age 17 by the end of the tax year". IT can be claimed by resident of US as well. It also states "The child must have an SSN to be a qualifying child eligible for the child tax credit (CTC) or the additional child tax credit (ACTC)."
