By Davide Barbuscia

NEW YORK Wall Street's focus is turning to at-risk U.S. Treasury debt payments as the deadline to raise the government's $31.4 trillion borrowing limit or risk default ticks closer.

U.S. Treasury Secretary Janet Yellen on Sunday said June 1 remained a "hard deadline" for raising the federal debt limit, with the odds quite low that the government will collect enough revenue to pay its bills through June 15, when more tax receipts are due.

Should the government fail to raise the current $31.4 trillion borrowing cap before it exhausts its cash and borrowing capacity, it could miss payments on some of its debt.

In June, the Treasury must pay over $1.3 trillion between T-bills and bond payments, including principal and interest, JPMorgan has estimated.

"Considering June 1 as the 'drop dead' date and assuming any technical default is short-lived, bills maturing in early- to mid-June appear to be most at risk of being the first to default if the debt ceiling is not raised," fixed income strategists at the bank said in a note last week.

"In addition to T-bills, Treasuries with maturities in the middle of June and December are also at risk of having a missed coupon/ principal payment," they said.

T-bills do not pay regular interest payments because their maturity dates are very short. Longer-term Treasury debt such as bonds and notes pay interest every six months.

Here is a list of next month’s total interest and principal payments due on Treasuries by payment date:

(Reporting by Davide Barbuscia; Editing by Lisa Shumaker)