The phrase "aides have asserted that" is correct and usable in written English.
It can be used when reporting statements or claims made by aides, typically in a formal or journalistic context.
Example: "According to the report, aides have asserted that the new policy will improve efficiency in the workplace."
Alternatives: "aides have claimed that" or "aides have stated that".
Mr. Gore and his aides have asserted that Mr. Bush's tax cut would gobble up surpluses and endanger prosperity.
Mr. Assad and his aides have asserted that the momentum of the conflict has turned in their favor since the Syrian military, aided by fighters from the Lebanese Shiite militant organization Hezbollah, routed rebel forces from the town of Qusayr near the Lebanon border this month.
Since the union first threatened to strike last year, the mayor and his aides have asserted that it was intentionally assisting the chairman of the Command Bus Company and Green Bus Lines, Jerome Cooper, as he continued to drive a hard bargain with the city -- a charge both Mr. Cooper and the union denied.
The Gore campaign and the campaign of Gov. George W. Bush of Texas have spent much of the last week trading bitter accusations that resemble the schoolyard chant, "I know you are, but what am I?" Mr. Gore and his aides have asserted that Mr. Bush, as a former oilman who has received large sums of campaign money from oil and gas companies, would be unable to stand up to oil-industry interests.
Aides to Bush have asserted that the president retains the authority to conduct surveillance without court permission.
Over many months, Mr. Trump has sought to raise questions about the health of Mrs. Clinton, 68, and his supporters have asserted that she is hiding something about her health (her aides have denied this).
Republican Senate aides have described Judge Massiah-Jackson as a better target because she is widely opposed by law-enforcement officials and prosecutors who have asserted that she is overly lenient on drug defendants.
A10 Prosecutor Criticizes Ex-Aide A federal prosecutor has asserted that I. Lewis Libby Jr., the former chief of staff to Vice President Dick Cheney, is trying to sabotage the criminal case against him by insisting that he be given sensitive government documents for his defense.
