Syrian dictator Bashar Assad must surrender his chemical weapons to avoid a U.S. military strike, but the U.S.-Russia framework on his disarmament makes no mention of Assad handing over his biological weapons.

"[T]he United States and the Russian Federation have committed to prepare and submit in the next few days to the Executive Council of the OPCW a draft decision setting down special procedures for expeditious destruction of the Syrian chemical weapons program and stringent verification thereof," the State Department framework explains.

"The United States and the Russian Federation believe that these extraordinary procedures are necessitated by the prior use of these weapons in Syria and the volatility of the Syrian civil war."

President Obama mentioned Assad's biological weapons when he laid down the red line last August. "We have been very clear to the Assad regime, but also to other players on the ground, that a red line for us is we start seeing a whole bunch of chemical weapons moving around or being utilized," he told reporters. "That would change my calculus. That would change my equation.”

White House press secretary Jay Carney demurred when asked about the place of biological weapons in the negotiations.

"What is obviously directly of concern here was the use of chemical weapons by the Assad regime," he told reporters Wednesday. "But I think that's a question that's worth following up on."

Sen. John Cornyn, R-Texas, pressed Kerry to include Assad's biological weapons in the disarmament agreement negotiated in Geneva, Switzerland, with Russian Foreign Minister Sergey Lavrov.

“Assad’s bioweapons, either in his hands or the hands of terrorists, represent a direct security threat to the U.S. and our allies," Cornyn wrote in a Friday letter. “Any credible agreement must force the surrender of both Assad’s bioweapons and chemical weapons, and it must achieve their destruction in a way that is workable, effective, timely, and verifiable.”