WASHINGTON – Suspected terrorists have changed how they communicate and have become more difficult to track as a result of former contractor Edward Snowden’s disclosures about U.S. surveillance operations, according to current and former officials who say that the changes have led to a significant loss of intelligence.

How much that loss amounts to remains unknown as the government’s classified assessment is continuing, they said.

In addition, Snowden’s disclosures about eavesdropping in Russia and China gave each of those countries insights that are already thought to have impaired the National Security Agency’s ability to intercept their communications, the officials said.

Among the disclosures from Snowden that were published in The Washington Post and the Guardian was that Skype, the Internet calling service, was among the systems that provided data to the NSA’s secret PRISM database. That disclosure contradicted a widespread belief that calls made via Skype were difficult or impossible to intercept.

Some alleged terrorists the NSA was tracking are no longer using Skype, U.S. officials say. Others have stopped using email, said one U.S. official who has been briefed on the damage.

The inability to use such common communications systems creates problems for terrorist groups by reducing their ability to share plans and coordinate, but it also costs intelligence agencies information, the official said.

Osama bin Laden had been savvy enough to take extreme measures to avoid emitting an electronic signature: his compound in Abbottabad, Pakistan, had no Internet or phone service, and his couriers took the batteries out of their cellphones when they approached within miles of the location. Most militants either can’t afford to be that careful or have simply not tried to, the official said.