Benghazi, Libya (CNN) -- Eyewitnesses in the embattled Libyan city of Misrata reported especially intense shelling by Moammar Gadhafi's forces overnight -- the heavy fire picking up at about the same time reports came out that one of the leader's son was killed in a NATO airstrike. "There's been continuous and heavy shelling for three hours straight," said one man, talking to CNN from about three miles from Misrata's city center Sunday. "There have been a lot of explosions." Heavy gun and artillery fire could also be heard early Sunday throughout Benghazi, which is the hub for rebel forces and their transitional government.
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NEW: Witnesses report heavy fire from Gadhafi forces in Misrata and Benghazi
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NEW: One man thinks it is "revenge" for a strike killing one of Gadhafi's sons
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NATO's leader reaffirms the mission, rejecting "any threat against Italy or any other ally"
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Earlier Saturday, Gadhafi called on NATO to end airstrikes targeting his forces
The @placeholder leader remained defiant, as he sharply criticized those behind the attacks and questioned their intent.