NEW YORK (CNN/Money) - A new study of employees worldwide finds that only 14 percent are fully engaged on the job and willing to put in extra effort for their companies.

The high levels of disengagement suggest that there is untapped "employee performance potential," according to Towers Perrin's HR Services, which conducted the survey.

In the United States, 21 percent of employees were fully engaged last year, not significantly changed from 22 percent in 2003.

"Employees in the United States feel they've hung in during the tough years," noted Julie Gebauer, Managing Director at Towers Perrin's HR Services. "They don't think they've seen enough in terms of pay raises, incentives or other rewards for their contributions -- despite hearing lots of talk about 'pay for performance.'"

The study found major differences in employee engagement across countries, with the highest levels in Brazil (31 percent) and Mexico (40 percent). The lowest levels were in the Asian countries in the survey -- South Korea (9 percent), China (8 percent), India (7 percent)and Japan (2 percent).

"For the first time ever, we've given a voice to the workforce worldwide," noted Donald Lowman, a Managing Director of Towers Perrin. "What we're hearing is that people want to contribute more. But they say their leaders unintentionally put obstacles in their paths."

Among the highly engaged employees, 84 percent reported that they thought they could positively impact their company's products, while only 31 percent of disengaged employees said the same.

Towers Perrin surveyed over 85,000 people working for large and midsize companies across 16 countries.

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