Story highlights Congress and Ukraine long sought anti-tank weapons in battle against separatists

It's another US development that Russia is expected to criticize

(CNN) The US is going to provide lethal anti-tank weapons to Ukraine to help it fight off separatists which have the backing of Russia, a senior State Department official told CNN.

The State Department officially announced Friday evening that the US was going to provide Ukraine with "enhanced defensive capabilities as part of our effort to help Ukraine build its long-term defense capacity, to defend its sovereignty and territorial integrity, and to deter further aggression," but the statement from spokeswoman Heather Nauert said it was not going to give any further details.

The State Department said the "US assistance is entirely defensive in nature, and as we have always said, Ukraine is a sovereign country and has a right to defend itself."

Among the weapons being sent are US-made Javelin anti-tank missiles, the official said.

Members of Congress and the US-backed Ukrainian government had long requested anti-tank weapons to boost Kiev in its fight against Russian-backed separatists.

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