Banks are doing a good job of meeting their customers' demands for modern, high-tech services, but they've got some work to do on the basics, a new survey found.

Customers are satisfied with banks' mobile and tech offerings, and with the convenience and connectivity they provide, according to the Consumer Banking Expectations Index released Tuesday by the banking-technology company FIS.

But banks in the U.S. are not meeting expectations for safety and security, which customers rank as their highest priorities, the survey said. Financial institutions also received low scores for fairness and transparency.

The results suggest serious concerns around issues like identity theft and the security of personal data, and show how high or hidden fees can damage a bank's reputation. More broadly, it indicates that customers have raised their standards for what they expect from financial institutions, and now banks need to catch up, said Anthony Jabbour, corporate executive vice president for FIS' financial solutions group.

"It's not that the banks are working any less at security or have deprioritized that, but consumers are continuing to raise their expectations," he said.

The index, the first of a planned annual series from FIS, is based on online responses from more than 9,000 retail customers in 9 countries, including 1,000 in the U.S. Respondents ranked the importance of 18 different attributes of their banking provider and rated their satisfaction in each category, which FIS then weighted to calculate overall satisfaction.

An average score of 100 means the customer is satisfied with his or her bank; banks can score above 100 if they exceed expectations. FIS also identified "performance gaps" — mismatches between a customer's expectation and what banks are delivering — by calculating the difference between the scores for importance and satisfaction.

The average satisfaction score for financial institutions in the U.S. was 80, suggesting that banks have problems meeting customers' needs. Only about one-third of respondents said their bank was meeting expectations — and most of these banked at smaller institutions.

In general, the larger the financial institution, the less satisfied the customer. Credit unions had the highest satisfaction score, at 91, of any type of institution, followed by community banks (86), large and midsize banks (79) and the four universal banks (72).

Quality in-person service was a huge boost for community banks, and ranked as the highest positive difference between expectation and satisfaction for any of the attributes FIS examined.

"The benefit for community banks is they live in the communities where their customers are and they know their needs and how to engage them," Jabbour said. "The larger they get, the more difficult it is to do that."

The challenge for U.S. banks goes beyond improving security. The low scores for fairness, transparency and reliability suggest that high or hidden fees do serious harm to banks' relationships with their customers. In general, customers "don't think that [financial] institutions deliver a fair and open deal," the study said.

The good news is that banks' investments in improving their tech offerings appear to be paying off. Connectivity, cross-channel service and digital payments all had positive performance gaps, FIS found. Yet Jabbour warns that banks need to keep investing in these services or risk failing to keep up with their customers' ever-rising expectations.

"It's great that today banks are meeting those expectations, but they have got to keep running," he said. "The expectations will rise dramatically."

Despite their problems, U.S. banks are still doing better than those in most other countries. American financial institutions had the second-highest satisfaction score of any nation's in this nine-country survey, behind only German banks, which scored 83. Customers in developing nations were generally less satisfied, with India (68), Brazil (64) and Thailand (62) scoring lower than the European and North American nations.