The impact of a leaked al-Qaeda terrorist plot has caused more immediate damage to US counterterrorism efforts than the thousands of classified documents disclosed by former National Security Agency (NSA) contractor Edward Snowden, US government analysts and senior officials say.
Since news reports in early August revealed that the US intercepted messages between Ayman al-Zawahiri, who succeeded Osama bin Laden as the al-Qaeda's head, and Nasser al-Wuhayshi, the head of the Yemen-based al-Qaeda in the Arabian Peninsula, discussing an imminent attack, analysts have detected a sharp drop in the terrorists' use of a major communications channel that authorities were monitoring.
Since August, senior US officials have been scrambling to find new ways to tap into al-Qaedea's electronic messages and conversations.
"The switches weren't turned off but there has been a real decrease in quality" of communications, said one US official, who like others quoted spoke on the condition of anonymity.
The drop in message traffic after the communication intercepts contrasts with what analysts describe as a far more muted impact on counterterrorism efforts from Snowden's disclosures of the broad capabilities of NSA surveillance programmes. Instead of terrorists moving away from electronic communications after those disclosures, analysts have detected terrorists mainly talking about the information Snowden has disclosed.
Senior US officials say that Snowden's disclosures have had a broader impact on national security in general. This includes fears that Russia and China now have more technical details about the programmes. Diplomatic ties have also been hurt.
The communication intercepts between Zawahiri and Wuhayshi revealed what US intelligence officials have described as one of the most serious plots against American and other Western interests since the September 11, 2001, attacks. It prompted the closure of 19 US embassies and consulates for a week, when the authorities concluded that the plot focused on the embassy in Yemen.
McClatchy Newspapers first reported on the conversations on August 4. Two days before that, The New York Times agreed to withhold the identities of the al-Qaeda leaders after senior US intelligence officials said the information could jeopardise their operations.
After the government became aware of the McClatchy article, it dropped its objections to the Times publishing the same information, and the newspaper did so on August 5.
US counterterrorism officials say they believe the disclosure has had a significant impact because it was a specific event that signalled to terrorists that a main communications network that the group's leaders were using was being monitored.
Snowden's disclosures have not had such specificity about terrorist communications networks that the government was monitoring, they said.