RIYADH — Palestinian President Mahmoud Abbas said on Sunday only the United States could stop Israel attacking the border city of Rafah in Gaza, adding that the assault, which he expects within days, could force much of the Palestinian population to flee the enclave.

“We call on the United States of America to ask Israel to not carry on the Rafah attack. America is the only country able to prevent Israel from committing this crime,” Abbas told a special meeting of the World Economic…