The White House is increasing pressure on Damascus to let a waiting UN team of chemicial weapons inspectors into Syria to probe allegations of chemical weapons use there.
Syrian President Bashar al-Assad requested the UN inspection after alleging that rebels had carried out a chemical attack.
But Assad has refused entry to the team because it also wants to inspect government facilities.
On April 29, UN Secretary-General Ban Ki-moon also urged Assad's regime to allow the UN team into the country. Ban said the inspectors need access for a "credible and comprehensive inquiry."
The team is led by Swedish scientist Ake Sellstrom. Assad's regime and the rebels have accused each other of using chemical weapons in Aleppo in March.
Ban says inspectors should also investigate allegations of a December chemical attack in Homs.
Based on reporting by Reuters, AP, and AFP