The United States (US) Department of Homeland Security announced steps on Monday to prevent the fraudulent use of H1B visas, used by employers to bring in specialised foreign workers temporarily, which appeared to fall short of President Donald Trump's campaign promises to overhaul the programme.

A White House official said Trump may still do more on the programme.

Trump had promised to end the lottery system for H1B visas, which gives each applicant an equal chance at 65,000 positions each year.

Lobbyists for businesses who rely on H1B visas, commonly used by the tech sector, had expected Trump to upend the lottery in favour of a system that prioritised workers who are highly skilled and would be highly paid in the US.

The lottery for fiscal year 2018 opened on Monday without changes.

The start of the lottery was seen by those watching the issue as the unofficial deadline for the Trump administration to enact H1B visa reform, and the failure to meet that deadline signals that Trump's promised overhaul of the system may be off the table or long delayed.

"More oversight is a good start, but employers can still use the program legally to depress wages and replace American workers. That falls short of the promises President Trump made to protect American workers," said Peter Robbio, a spokesman for Numbers USA, a Washington-based group that advocates for limiting immigration into the United States.

The Trump administration has taken other steps to crackdown on H1B visa abuse, such as issuing a Justice Department warning to employers and announcing plans to increase transparency on applicants.

"These are important first steps to bring more accountability and transparency to the H1B system," a White House official said.

"The administration is considering several additional options for the president to use his existing authority to ensure federal agencies more rigorously enforce all aspects of the program."

Tech companies rely on the programme to bring in workers with special skills and have lobbied for an expansion of the number of H1B visas awarded.

Proponents of limiting legal immigration, including Trump's senior adviser Stephen Miller, have argued the program gives jobs that Americans could fill to foreign workers at a less expensive cost.

The measures announced by DHS on Monday focus on site visits by US authorities to employers who use H1B visas.

In future site visits, US Citizenship and Immigration Services agents will investigate incidents where an employer's basic business information cannot be validated; businesses that have a high ratio of H1B employees compared with US workers; and employers petitioning for H1B workers who work off-site.