By JOHN HEILPRIN and ZEINA KARAM

BEIRUT (AP) — A U.N. investigation has concluded that Syrian forces committed crimes against humanity by killing and torturing hundreds of children, including a 2-year-old girl reportedly shot to death so she wouldn't grow up to be a demonstrator.

The results of the inquiry, released on Monday, added to mounting international pressure on President Bashar Assad, a day after the Arab League approved sweeping sanctions to push his embattled regime to end the violence. Syria's foreign minister called the Arab move "a declaration of economic war" and warned of retaliation.

The report by a U.N. Human Rights Council panel found that at least 256 children were killed by government forces between mid-March and early November, some of them tortured to death.

"Torture was applied equally to adults and children," said the assessment, released in Geneva. "Numerous testimonies indicated that boys were subjected to sexual torture in places of detention in front of adult men."

The U.N. defines a child as anyone under the age of 18. The report was compiled by a panel of independent experts who were not allowed into Syria. However, the commission interviewed 223 victims and witnesses, including defectors from Syria's military and security forces.

The panel said government forces were given "shoot to kill" orders to crush demonstrations. Some troops "shot indiscriminately at unarmed protesters," while snipers targeted others in the upper body or head, it said.

It quoted one former soldier who said he decided to defect after witnessing an officer shoot a 2-year-old girl in Latakia, then claim he killed her so she wouldn't grow up to be a demonstrator.

The list of alleged crimes committed by Syrian forces "include murder, torture, rape and other forms of sexual violence," said the panel's chairman, Paulo Sergio Pinheiro, a Brazilian professor. "We have a very solid body of evidence."

At least 3,500 people have been killed since March in Syria, according to the U.N. — the bloodiest regime response against the Arab Spring protests sweeping the Middle East. Deaths in Egypt, Tunisia and Yemen have numbered in the hundreds; while Libya's toll is unknown and likely higher, the conflict there differs from Syria's because it descended into outright civil war between two armed sides.

The U.N. investigation is the latest in a growing wave of international measures pressuring Damascus to end its crackdown, and comes on the heels of sweeping sanctions approved Sunday by the Arab League.

Syrian officials did not comment directly on the U.N. findings. However, the regime reacted sharply to the Arab sanctions, betraying a deep concern over the economic impact and warning that Syria could strike back.

Foreign Minister Walid al-Moallem called the Arab League action "a declaration of economic war" and said Syria had withdrawn 95 percent of its assets in Arab countries.

Economy Minister Mohammed Nidal al-Shaar said "sources of foreign currency would be affected" by the sanctions, reflecting concerns that Arab investment in Syria will fall off and transfers from Syrians living in other Arab countries will drop.

Al-Moallem said Syria had means to retaliate.

"Sanctions are a two-way street," he warned in a televised news conference.

"We don't want to threaten anyone, but we will defend the interests of our people," he added, suggesting Syria might use its position as a geographical keystone in the heart of the Middle East to disrupt trade between Arab countries.

Chaos in Syria could send unsettling ripples across the region.

Syria borders five countries with whom it shares religious and ethnic minorities. As they struggled with ways to respond to Assad's brutal crackdown, world leaders have been all too aware of the country's web of allegiances, which extend to Lebanon's powerful Hezbollah movement and Iran's Shiite theocracy.

The latest sanctions include cutting off transactions with Syria's central bank, and are expected to squeeze an ailing economy that already is under sanctions by the U.S. and the European Union. The net effect of the Arab sanctions could deal a crippling blow to Syria's economy.

"We've always said that global sanctions, without Arab sanctions, will not be as effective," said Said Hirsh, Mideast economist with Capital Economics in London.

Some 60 percent of Syria's exports go to Arab countries, and analysts concede the sanctions' effectiveness will hinge largely on whether Arab countries enforce them.

Iraq and Lebanon, which abstained from the Arab League vote, may continue to be markets for Syrian goods, in defiance of the sanctions. Syria shares long borders with both countries and moving goods in and out would be easy.

Still, there is no question the uprising is eviscerating Syria's economy. Hirsh said forecasts indicate it will contract by 5 percent this year and could shrink by another 10 percent in 2012 if sanctions are enforced and the Assad regime stays in power.

The economic troubles threaten the business community and prosperous merchant classes that are key to propping up the regime. An influential bloc, the business leaders have long traded political freedoms for economic privileges.

The opposition has tried to rally these largely silent, but hugely important, sectors of society. But Assad's opponents have failed so far to galvanize support in Damascus and Aleppo — the two economic centers in Syria.

The Arab sanctions, however, could chip away at their resolve.

Since the revolt began, the Assad regime has blamed the bloodshed on terrorists acting out a foreign conspiracy to divide and undermine Syria. Until recently, most deaths appeared to be caused by security forces firing on mainly peaceful protests. But lately, there have been growing reports of army defectors and armed civilians fighting Assad's forces — a development that some say plays into the regime's hands by giving government troops a pretext to crack down with overwhelming force.

The Assad regime has responded to the street protests by sheer brutal force while at the same time announcing reforms largely dismissed by the opposition as too little too late.

On Monday, a spokesman for a committee tasked with drawing up a new constitution said it would recommend the abolishment of Article 8 which states that the ruling Baath Party is the leader of the state and society.

The article's abolishment was once a key demand of the protest movement. However, such overtures are now unlikely to satisfy opposition leaders who say they will accept nothing more than the downfall of the regime.

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Heilprin reported from Geneva. AP Business Writer Tarek El-Tablawy contributed to this report from Cairo.