The number of students in the United States from China, Iran and Saudi Arabia has risen sharply in the past year, giving a boost to US universities and the economy, a study said Tuesday.

The United States was home to nearly 765,000 international students in 2011-2012, a growth of 5.7 percent from the previous academic year and part of a decade-long increase, according to the Institute of International Education.

China accounts for much of the growth, with the number of Chinese students going up more than 23 percent. More than one-quarter of the international students in the United States are Chinese, the non-profit group said.

"China has a very rapidly growing middle class that is able to send their children anywhere in the world for the best education," said Peggy Blumenthal, senior counselor to the institute's president.

The most popular fields for Chinese students are business and engineering, with many of them looking for lucrative careers back home in companies or government, the institute found.

India and South Korea were the second and third largest sources of students to the United States, although their numbers went down slightly.

But Saudi Arabia and Iran saw huge growth, with a more than 50 percent increase in Saudi students and the number of Iranian students rising by nearly one-quarter.

The Saudi government has launched a major push to send students overseas, more than a decade after the September 11 attacks on the United States in which 15 of the 19 hijackers were Saudi nationals.

Despite tense US ties with Iran and a lack of diplomatic relations, President Barack Obama's administration moved last year to make it easier for Iranian students by issuing two-year, multiple-entry visas.

"Because of the deteriorating situation in Iran, many families want to get their college-aged children out of the country and into a safe place and into a good academic environment," Blumenthal said.

"The US government has made a real effort to encourage Iranian students to come. They see these as the future leaders of the country -- in 10, 20 years, Iran may be a very different place," she said.

The Commerce Department found that foreign students -- most of whom rely on family funds or working -- contributed $22.7 billion to the US economy last year through tuition and related expenses.

The United States plays host to more foreign students than any other country, although only four percent of its enrollment comes from overseas.

By contrast, Britain -- the second biggest host of international students -- and Australia both have student bodies that are roughly 20 percent international.