The report said 93 percent of those accounts were flagged using its own internal, proprietary tools, and 74 percent were suspended before posting their first tweet -- but the company did not say how those accounts were caught and flagged.
Breaking that figure down, the company said in the last six months of 2017, the company permanently closed 274,460 accounts for violating its rules related to the promotion of terrorism.
That's down by over 8 percent at the last count in September, in which the site suspended 299,000 accounts linked to terrorism in first half of 2017.
"We continue to see the positive, significant impact of years of hard work making our site an undesirable place for those seeking to promote terrorism, resulting in this type of activity increasingly shifting away from Twitter," said the report.
Less than 0.2 percent of those suspensions are as a result of governments filing reports with the company, it said.
In other words, Twitter says it has for the most part a handle on keeping particular terrorist content off its platform.
Governments remain keen on pushing a counter-terror strategy that involves applying pressure on social media giants, seen by primarily politicians as the root cause of terror propaganda. British prime minister Theresa May and French president Emmanuel Macron have in the past year suggested fining companies that fail to swiftly remove terrorist material from their services, which they say offers "safe spaces" for terrorists and criminals.
Facebook, Microsoft, Twitter, and YouTube announced in late 2016 the new so-called Global Internet Forum to Counter Terrorism, which the companies will use to "share technological and operational elements" of their respective individual efforts to combat terrorist content.
The firms said the forum will, among other things, store a shared database of hashes for terrorist propaganda video and imagery that have been removed from their services, with the aim of flagging re-uploaded content.
Also in Twitter's latest transparency report, the company said that it received 6,268 demands affecting 16,861 accounts from governments for the second half of the year, resulting in the handover of some data in 55 percent of cases.