Ongoing crisis in Syria has intensified near Aleppo, the largest city in the country. Rebel forces gained control over parts of the area, though the situation on the ground remains fluid.
Martin Indyk, director of the foreign policy program at the Brookings Institution, testified before a U.S. Senate committee that the regime in Damascus is facing a "kill or be killed" scenario.
U.N. officials and humanitarian groups allege Syrian forces, with the blessing of government officials, likely committed war crimes during the conflict. It's "impossible to imagine" that the regime can withstand growing opposition, said Indyk.
"The Syrian army will likely crack under the strain of prolonged conflict with its own citizens," he added.
Some members of the U.N. Security Council expressed opposition to a formal resolution condemning Damascus for fear of further militarization of the conflict.
U.N. Secretary General Ban Ki-moon announced Thursday that former Secretary-General Kofi Annan has resigned as the special peace envoy to Syria. He said the hand that was extended for peace has been turned away.
"Both the government and the opposition forces continue to demonstrate their determination to rely on ever-increasing violence," he said in a statement.
2014: The Year in Music [PHOTOS]