- NEW: Opposition leaders are meeting in Egypt, but some members withdraw
- Report: Syria's Bashar al-Assad says he regrets the shooting down of a Turkish plane
- Rebel official: At least 258 members of regime forces and their relatives have fled
- A child describes being shocked with electricity and having a toenail ripped out
(CNN) -- Global disgust over the Syrian regime's purported torture of citizens reached a pinnacle Tuesday, with a human rights group and a foreign diplomat decrying new reports of government atrocities.
According to a report published Tuesday by Human Rights Watch, the Syrian regime has been carrying out "a state policy of torture" as part of an effort to crush dissent. The group cited more than 200 former prisoners and security officers who defected.
Authorities are using a network of torture chambers "to intimidate and punish people who dare to oppose the government," said Ole Solvang, a Human Rights Watch researcher.
In some cases, the report said, the government tortured children.
"They electrocuted me on my stomach, with a prod. I fell unconscious," said Hossam, a 13-year-old boy who told Human Rights Watch he was detained in the town of Tal Kalakh. "When they interrogated me the second time, they beat me and electrocuted me again. The third time, they had some pliers and they pulled out my toenail."
CNN has also interviewed more than a dozen Syrians who described beatings, electrocution and horribly crowded conditions in prison cells.
The Syrian government has routinely denied allegations of abuses. Recently, Syria's ambassador to the United Nations walked out of a meeting of the U.N. Human Rights Council in protest after the Syrian regime was accused of committing crimes against humanity.
But British Foreign Secretary William Hague said he welcomed the Human Rights Watch report.
"It highlights the horror of what is happening. The scale of the barbaric acts that are being carried out by the regime against the population is appalling," Hague said in a statement Tuesday.
But Syrian President Bashar al-Assad's forces are showing signs of fracture, with growing reports of defections.
At least 258 people, including soldiers, officers and their relatives, fled Monday, said Col. Malek Kurdi, deputy commander of the rebel Free Syrian Army.
Kurdi said it was not yet certain how many were soldiers and how many were relatives.
Thousands of Syrians have escaped to Turkey, whose relations with Syria deteriorated after Syria recently shot down a Turkish military jet.
But in an interview with Turkey's Cumhuriyet newspaper, al-Assad expressed regret over the downing.
"I would not wish it for any plane other than an enemy one," al-Assad said in the Tuesday article. "Especially for a Turkish plane, I say (a) hundred percent, 'If only it did not happen.' "
He said the course of the Turkish plane was "on the same course that Israeli planes attempted to enter our airspace three times before. Therefore, a plane coming from that side is perceived by the Syrian military as an Israeli plane. It was accepted as an enemy plane, reacted against fast and fired at."
A search for the pilots of the downed jet was ongoing. The wreckage of the plane has not yet been located.
Meanwhile, opposition groups were set to meet for a second day Tuesday in Cairo, Egypt, in an attempt to unify their platform.
But some members of at least one key group withdrew from the discussions.
Leaders of the Syrian Revolution General Commission -- a coalition of more than 40 opposition groups -- walked out in part because some of the groups in Cairo are willing to have a dialogue with the current regime, said Rania Kisar, a member of the coalition.
Kisaralso said the agenda in Cairo did not including supporting the Free Syrian Army.
Unlike the prominent Syrian National Council opposition body -- which is composed largely of expatriates -- the Syrian Revolution General Commission is based within Syria and has members directly involved in the day-to-day conflict.
Across the country Tuesday, the government launched new attacks on cities, opposition activists said.
"The regime's army waged a raid-and-arrest campaign ... amid a crippling siege" in a neighborhood of Hama, the Local Coordination Committees of Syria said.
Fresh shelling also landed in the besieged city of Homs and in Deir Ezzor, the opposition group said.
The carnage in Syria has spiked in the past two days, with at least 109 people killed Sunday and 114 people killed Monday, opposition activists said.
Over the past 16 months, the Syrian government has insisted it is fighting the vaguely defined "armed terrorist groups."
CNN cannot independently confirm the reports of casualties or violence because Syria restricts access by international journalists.
CNN's Ivan Watson, Salma Abdelaziz, Holly Yan and Yesim Comert contributed to this report.
