London: UN Secretary-general Ban Ki-moon denounced on Wednesday the "escalating violence" in Syria, and called on authorities there to "immediately" stop the bloody repression.

"The secretary general is following with deep concern the escalating violence against peaceful protesters in Syria," said spokesman Martin Nesirky, who called on the government to "stop the repression immediately".

"The secretary-general reiterates his call for a credible and inclusive dialogue, which should be carried out without delay," Nesirky said.

Meanwhile, Human Rights Watch said Syria's government has stepped up the arrest of anti-government demonstrators even as it engages in a so-called national dialogue with opponents.

At least 2,000 protesters have been detained since the end of June in the cities of Homs and Hama and in the suburbs of Damascus, and arrests have continued since the talks began July 10, the rights group said in an e-mailed statement late on Wednesday.

"President Al Assad talks reform but continues to practice repression, not only through the widespread killings of demonstrators but also through mass arrests," Sarah Leah Whitson, Middle East director at Human Rights Watch, said in the statement.

A committee of Syrian intellectuals and academics, convened by Al Assad to hold the national dialogue, called for a full review of the constitution earlier this month.