SINGAPORE — U.S. companies aren't likely to pack up their manufacturing operations in China and move them back home amid the trade war between Washington and Beijing, according to a prominent economist.

That's because supply chains are "very difficult to put together, and equally difficult to disentangle," said Stephen Roach, a senior fellow at Yale University.

Still, several American firms have made plans to diversify their production beyond China since the trade war started last year. But few have said they intend to completely leave China – or move all of their manufacturing back to the U.S. as President Donald Trump often says will happen.

"Clearly some components ... part of the source can be pulled out of China and into other countries. But to take an iPhone and bring the iPhone back home, forget it, just not going to happen in a way that would provide affordable product for American users of that device," Roach said at the Morgan Stanley Asia Pacific Summit in Singapore last week.