The phrase "a fierce attack on" is correct and usable in written English.
It can be used when describing a strong criticism or condemnation directed towards a person, idea, or action.
Example: "The article was a fierce attack on the government's handling of the crisis."
Alternatives: "a strong criticism of" or "a vehement condemnation of".
Labour launched a fierce attack on Osborne's plan this morning.
On Wednesday morning fighting broke out again as Mr Ouattara's troops launched a fierce attack on Mr Gbagbo's refuge.
The Macedonian government has today launched a fierce attack on northern villages held by ethnic Albanian insurgents.
But talks on that broke down, and on Friday the government opened a fierce attack on Aracinovo.
In their letter they assure Kiir of their goodwill, then launch into a fierce attack on almost every aspect of his government's record.
It's been coming: Alfie Brown's show last year – a fierce attack on comedy and our cultural life – was a shot across the bow.
He launched a particularly fierce attack on Sam Pitroda, a close aide of the Congress government who is credited with being the father of the Indian telecom revolution.
A fierce attack has been launched on David Bernstein by the League Managers Associationn after the former Football Association chairman claimed that coaches were setting a "terrible example" by their behaviour.
In an unusually fierce attack on the City Council, Mayor Rudolph W. Giuliani threatened yesterday to build new homeless shelters in the districts of members who were pushing a bill to give the Council more authority over his homeless policies.
Plans for a law allowing voters to sack misbehaving MPs, included in the Queen's speech, came under fierce attack on Wednesday with one prominent Conservative backbencher claiming it has been watered down to such an extent that the first time it is utilised, people will realise they have been duped.
"On the contrary, he's been accused that the chief minister's office did not respond to distress calls [during the riots]." He said the dramatic scene set in Kashmir, where Mr Modi and the soldiers come under fierce attack on a bridge while he waves a gigantic Indian flag, was an attempt to fit elements of the leader's past into his party's contemporary political narrative.
