By Niket Nishant and Jaiveer Shekhawat

(Reuters) -Comerica and Huntington Bancshares on Friday sharply cut their interest income growth forecasts for 2023, the latest U.S. banks to sound the alarm over faltering loan demand and a rise in deposit costs.

The Federal Reserve's fastest monetary tightening cycle since the 1980s helped lift lenders' net interest income in the second quarter, but the high rates are forcing some customers to rethink taking loans and buying big-ticket items.

NII - the difference between what banks make on loans and pay out on deposits - rose for nearly all lenders reporting earnings for the April-June quarter, with Comerica and Huntington also topping profit estimates.

But the high interest rate environment is also forcing lenders to boost deposit rates to prevent clients' money from fleeing to high-yielding alternatives like money market funds, and that will weigh on NII going forward, analysts have said.

Mid-sized lender Regions Financial, which also reported results on Friday, said its deposit costs had risen in the second quarter.

Comerica slashed its 2023 NII growth forecast to a range of 1% to 2% from 6% to 7% estimated earlier, and its shares fell 3.8%.

Huntington expects its NII to increase between 3% and 5% this year, compared with its prior expectation of a 6% to 9% growth.

Regions Financial kept its 2023 NII forecast unchanged but its stock declined 3.4%. "We still think there's a fair amount of caution in banks and there probably should be," said Christopher Marinac, director of research at wealth management firm Janney Montgomery Scott.

The industry, which is recovering from the aftershocks of a crisis sparked by the collapse of three mid-sized lenders earlier this year, is waiting to fund a potential increase in capital requirements and is holding off on buyback plans.

"Once we have some degree of certainty that we can hit our targets based on the new rules, I think that would put us in a position to really start thinking about share buyback," Comerica CFO James Herzog said on a post-earnings call.

The KBW Regional Banking Index was down nearly 1%, though still on track for its biggest weekly gain since January 2022, after a string of positive earnings reports from earlier this week helped bolster sentiment.

(Reporting by Niket Nishant, Jaiveer Singh Shekhawat and Sri Hari N S in Bengaluru; Editing by Devika Syamnath and Sriraj Kalluvila)