Unlocked 2GP org dependant package

Question

I'am trying to call a apex class method from another apex class which is a part of unlocked org dependant package.

Below is the class in package (Class is present as a part of installed package):

global with sharing class AccountUtil {
    global AccountUtil() {

    }
    
    global static List<Account> getFewAccounts() {
        return AccountUtil2.getSomeAccounts();
    }
    
 }

Class which is outside of unlocked package which does not have any namespace :

global class AccountUtil2 {
    
    global AccountUtil2() {
        
    }

    global static List<Account> getSomeAccounts() {
        return [SELECT Name FROM Account LIMIT 3];
    }
    
    global List<Account> getAccounts() {
        return [SELECT Name FROM Account LIMIT 3];
    }
}

When I execute namespace.AccountUtil.getFewAccounts(); in Anonymous window , it shows below error :

Dependent class is invalid and needs recompilation: Class namespace.AccountUtil : Variable does not exist: AccountUtil2

Is there a restriction which says that apex classes outside of unlocked, org dependant classes cannot be referenced inside the package?

Use case - We are in the process of converting large codebase into unlocked, org dependant packages gradually. Hence, this becomes important to create namespaces in modularised way.