(Reuters) - The U.S. Treasury Department is anticipating sending the first wave of $600 stimulus checks to U.S. individuals and households as early as this week, as previously planned, a senior Treasury official said on Monday. The Treasury would also send top-up payments to those who have already been issued checks if Congress increases the amount as President Donald Trump has demanded. On Sunday, Trump signed a $2.3 trillion pandemic aid and government spending package, passed the previous week, after threatening to block it unless lawmakers agreed to increase the payments to $2,000.