China says it has the right to block websites that break its laws after being accused of restarting the practice it halted during the August Olympic Games as part of a promise to widen media freedom.
Foreign Ministry spokesman Liu Jianchao said that certain websites had breached Chinese law by recognising "two Chinas" - a reference to Taiwan.
Liu would not say whether any websites had been censored.
The BBC reported that China appeared to have banned a number of foreign websites recently, including its Chinese-language news site and Voice of America in Chinese.
The sites had been unblocked after journalists attending the Beijing Olympics complained that the Government was censoring sites deemed sensitive.