(CNN) The Trump administration is expected to pull out of the "Open Skies" treaty -- which allows unarmed surveillance flights over American, Russian and several other countries' territories -- in a move that congressional Democrats warned would be a "gift" to Russian President Vladimir Putin.

It is believed the White House will make the announcement soon, a US official told CNN.

Here's a look at what's at involved.

What is the "Open Skies" treaty?

The treaty allows 34 countries to conduct unarmed surveillance flights over one another's territories -- including the US and Russia. It was signed in 1992 and went into effect in 2002.

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