Bynes Attacks Bass: You're an Ugly Ex Boy Bander

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In the wake of Amanda Bynes' recent arrest, displays of erratic public behavior and Twitter rants, longtime friend Lance Bass took to Las Vegas' Mark & Mercedes 94.1  radio show on Wednesday to speak out about his concern for the troubled starlet, which in turn ignited an all-out Twitter war.

"It's one of those situations where obviously there's some mental problems there and she's not able to see that," Bass, 34, said of the 27-year-old actress. "We all are [able to see it]," he told the radio show.

RELATED PICS: Amanda Bynes Twitter Photo Album

He added, "I'm actually really scared for her, and I hope someone is able to get to her to give her the help she needs."

In response, the What I Like About You actress attacked the former 'N Sync member, tweeting: "I ignored Lance Bass on Twitter and now he is saying I have a mental illness. Sorry you're an ugly ex boy band member w/ no talent or career."

Bass tweeted in response: "Ouch- The Amanda I know would never had said something like this to me- either this is a fake person or she really does have a mental illness. Way too sad. I reached out- all i can do,"

The online war of words continued with Bynes biting back: "I haven't spoken to Lance Bass in 11 years. To say I have a mental illness out of nowhere makes me lash out! You're making me crazy!"

Bass reacted: "Now I really don't think this is Amanda- we shot LoveWrecked together 7 years ago and she was just at my bday party 3 years ago. Hmmm 11?"

Bass and Bynes became friends when the former boy band member produced Love Wrecked in 2005, a romantic comedy in which Bynes played the lead.

RELATED: Courtney Love Calls Out Amanda Bynes

The Hairspray starlet has been a hot topic following her arrest last week in NYC for allegedly smoking marijuana in the lobby of her Manhattan apartment building and then throwing a bong out the window when police entered. She has since been released from jail.