Secretary of State Hillary Clinton says the United States is increasing its efforts to help Syrian rebels fighting to topple President Bashar al-Assad.

Clinton gave no details, but she said Tuesday that the U.S. is giving such non-lethal aid as medical and communications support. She said Washington is working outside of the U.N. Security Council, where Russia and China have vetoed three resolutions that would have taken strong action against the Assad government.

The secretary said the Syrian opposition is seizing control of more and more territory, which she says will eventually become a safe haven and a base for more operations. She said the opposition must be ready to start work on an interim government that protects the rights of all Syrians and safeguards the stockpile of chemical and biological weapons.

Syrian opposition activists say government forces raided several Damascus neighborhoods Tuesday and shelled other regions, including the southern town of Herak. At least six children were reported killed.