A group of lawmakers in the United States said on Monday they had requested more information from President Donald Trump's administration about the potential sale of precision-guided munitions to Saudi Arabia, expressing concern about civilian casualties in Riyadh's campaign in Yemen that delayed the deal last year.

Thirty mostly Democratic lawmakers signed the letter to US Secretary of State, Rex Tillerson, and Secretary of Defence, James Mattis, citing expectations that the administration plans to go ahead with the sale.

"As you know, the previous administration made the decision in December 2016 to halt a planned sale of precision-guided munitions (PGM) to Saudi Arabia due to concerns over widespread civilian casualties and significant deficiencies in RSAF's (the Saudi Air Force's) targeting capabilities," the letter, dated Friday but released on Monday, said.

"According to recent reports, however, the State Department has now reversed course and removed the suspension on these PGM sales," they said in the letter, led by Representative Ted Lieu, a Democratic member of the House Foreign Affairs Committee.

The State and Defense Departments do not comment on planned arms sales before formal notification is sent to Congress.

In December, then-President Barack Obama's administration decided to halt the sale of the systems, manufactured by Raytheon Co, that convert bombs into precision-guided munitions because of concerns about the extent of civilian casualties during Saudi Arabia's campaign in Yemen.

Congressional aides told Reuters the Trump administration was on the verge of sending a formal notification to Congress about the sale, which would trigger the formal 30-day review to allow members of Congress to attempt to pass legislation to stop any sale.

Trump has said he wants to clear the way for US arms sales abroad, to bolster efforts by US partners to fight militant groups and help create US jobs.

His administration recently told Congress it also planned to pursue sales to Bahrain and Nigeria that had been delayed under Obama by human rights concerns.

Congressional aides said they expected an effort to pass legislation to stop the PGM sale. However, such legislation has never succeeded. A measure seeking to block the sale of tanks to Riyadh failed in September.

"It is in our national security interest as well as that of our Saudi partners ─ to ensure that the RSAF has the ability to avoid civilian casualties before the U.S. sells them any additional air-to-ground munitions," the letter said.-REUTERS