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“Active and comprehensive discussions” are underway in the Obama administration over whether the United States should provide heavy weapons to Ukrainian forces under increasing attack by pro-Russian separatists, senior defense officials told NBC News on Monday.

The most lethal weapons could include anti-armor missiles, armored Humvees, radar and drones to attack Russian rocket launchers and artillery that have been battering Ukrainian forces, the officials said.

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They stressed Monday that no decision had been made. The New York Times reported Sunday that administration and military officials are edging toward providing “defensive” arms to Ukrainian forces.

Bernadette Meehan, a spokeswoman for the National Security Council, said that the administration is “constantly assessing” its options but declined to discuss the details of administration policy debates.

Fighting in eastern Ukraine has intensified in recent weeks, and peace talks collapsed over the weekend. A rebel leader told Russian media on Monday that the rebels want to boost their fighting force to 100,000. The current number is about 9,000, according to the Ukrainian president.

The Pentagon is reviewing the question “cautiously,” one official said. There is concern that providing heavy weapons to Ukraine would only escalate the fighting and increase instability. For that reason, “As of now no one here is pounding the table to provide heavy weapons,” the official said.

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— Jim Miklaszewski and Kristen Welker