"merciless attack" is a correct and usable phrase in written English.
You can use it to describe a situation where someone was attacked very harshly, with no mercy shown. For example, "The dictator's forces launched a merciless attack on the civilians".
Over the past three decades, workers have been under merciless attack.
Last week, Mr. Lepper unleashed a merciless attack on Mr. Cimoszewicz, calling him "a scoundrel".
"It was a merciless attack," Fernando Aristizabal, a top state official told Colombia's Caracol Radio.
But what sets it apart is its merciless attack on consumer culture in sequences brutal, comic and brutally comic.
A group of teenagers who hunted down and killed another schoolboy in a brazen and merciless attack face jail.
North Korea on Friday threatened to "start a merciless attack" against South Korea if activists there send balloons across the border bearing propaganda leaflets, as they have pledged to do on Monday.
He and his lawyers launched merciless attacks on the Islamic republic's more archaic and repressive institutions.
The next day The Inquirer began a series of merciless attacks on the candidate, involving misleading headlines, distorted news stories and vitriolic editorial comment.
And, in terms of personal approval ratings, Cameron was running well ahead of Miliband, a reserved and untested forty-five-year-old who has been subjected to merciless attacks by the Tory media.
North Korea threatens "merciless" attacks on U.S. forces as they beef up presence in the region.
Given Bannon's dualist view of society, Breitbart's merciless attacks against religious and cultural opponents make sense.
