The United Nations on Monday raised its estimate of the number of protesters killed in the Syrian uprising to 2,600, as it announced the appointment of three investigators to look into human rights abuses in the country, where President Bashar al-Assad has defied international condemnation of the crackdown, even among his dwindling allies.

The new death estimate, by the United Nations Human Rights Council, came three weeks after the council convened an emergency session at its Geneva headquarters and called on Mr. Assad to end the crackdown on the uprising, which began in March against his family’s four decades in power. The council’s estimate of Syrian deaths during the protests had been 2,400 through mid-August, suggesting that Mr. Assad has not eased his tough stance.

Navi Pillay, the High Commissioner for Human Rights, told reporters in Geneva that “the situation in Syria is still dire.”

The three-member panel appointed to investigate Syrian abuses will be led by Sérgio Pinheiro of Brazil, the former United Nations investigator of political repression in Myanmar. The other two members are Yakin Erturk of Turkey, a sociology professor and an authority on women’s rights, and Karen Abu Zayd, an American who is the former head of the United Nations agency that administers relief to Palestinian refugees.