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The Syrian army shelled residential areas and unleashed gunmen Wednesday, and a human rights group said at least 18 people were killed, including an 8-year-old boy -- evoking memories of the Assad regime's brutal, 40-year legacy of crushing dissent.

Syrian activists and protesters involved in the seven-week-long uprising renewed their cries for the world to join them in calling for embattled President Bashar Assad to give up power.

"The Syrian people are being killed and Bashar knows that he has a free hand. Nobody is really stopping him," a 28-year-old Syrian from the besieged seaside city of Banias told The Associated Press by telephone, asking that his name not be used out of fear for his own safety.

Assad is determined to crush the uprising despite international pressure and sanctions from Europe and the United States. European countries summoned Syrian ambassadors Wednesday to threaten a new round of sanctions if the regime fails to halt the bloodshed.

But rights activists brushed off the threats as ineffective, saying the death toll already has exceeded those seen during the recent uprisings in Yemen and Tunisia.

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"It is clear the international community is still giving the regime chances," said Rami Abdul-Rahman, director of the Syrian Observatory for Human Rights.

More than 750 people have been killed and thousands detained since the uprising began in mid-March, touched off by the arrest of teenagers who scrawled anti-regime graffiti on a wall.

Obama administration officials said Tuesday the U.S. is edging closer to calling for an end to the long rule of the Assad family. The officials said the first step would be to say for the first time that Assad has forfeited his legitimacy to rule, a major policy shift.

In recent weeks, Assad has dispatched soldiers backed by army tanks and snipers across the country, saying security forces are rooting out "armed terrorist groups" and thugs.

On Wednesday, the army shelled three neighborhoods in Homs, the country's third-largest city and home to one of Syria's two oil refineries. Shelling and heavy gunfire also were reported in the villages of al-Haraa, Inkhil and Tafas outside Daraa, the southern city where the uprising began.

Ammar Qurabi, head of the National Organization for Human Rights in Syria, said 13 people were killed in al-Haraa, including the 8-year-old boy, and five were killed in the central city of Homs. Most were killed in shelling, but gunfire killed several of the victims, he said.

"There were loud explosions and gunfire from automatic rifles throughout the night and until this morning," a Homs resident told the AP by telephone, asking that his name not be used for fear of government reprisal. "The area is totally besieged. We are being shelled."

Homs has seen some of the largest anti-government demonstrations.

Few details were leaking out of the Daraa area and calls were not going through to the city, which was the site of a recent military siege as tanks and snipers tried to crush the heart of the revolt. A media blackout has prevented independent assessments of the situation in Syria.

Earlier Wednesday, U.N. chief Ban Ki-moon urged Syria to allow an international aid assessment team to enter Daraa. He told reporters in Geneva he is disappointed the assessment team "has not yet been given the access it needs."

UNRWA, the U.N. group that aids Palestinian refugees, has nearly suspended its assistance to refugees in southern Syria because of the unrest there, said UNRWA spokesman Chris Gunness.

About 50,000 registered refugees in Daraa, Homs and the surrounding areas have been cut off from the regular aid provided by the U.N. group.

Shelling residential areas was a tactic used by Assad's father and predecessor, Hafez. In 1982, the elder Assad crushed a Sunni uprising by shelling the town of Hama, killing 10,000 to 25,000 people, according to Amnesty International estimates.

Conflicting figures exist and the Syrian government has made no official estimate. For the next two decades, until his death, Hafez Assad ruled uncontested and the shelling was seared into the minds of Syrians.

Bashar Assad has not done anything on the scale of the Hama killings in his 11 years in power. Witnesses have reported the shelling of neighborhoods in recent weeks, but the four-hour-long siege in Homs was the most intense and signaled the government was stepping up its efforts to intimidate the population.

In addition to the crackdown, Assad has announced a series of reforms that have been widely viewed as symbolic overtures to appease protesters.

State-run TV said Wednesday the government formed a committee to come up with a new election law that would be "up to international standards."

Before the uprising, such a declaration would have been unthinkable in a country with harsh restrictions who is allowed to run. Assad himself inherited power from his father in 2000 after an election in which he was the only candidate.

But Syrians' demands have snowballed as the uprising gained momentum.

The international community also has condemned the crackdown.

The European Union already has decided to impose sanctions on 13 Syrian officials, prohibiting them from traveling anywhere in the 27-nation bloc. But the first round of sanctions doesn't target Assad himself.

If a new round of sanctions comes down targeting the president, it would be a humiliating personal blow to Assad, a 45-year-old eye doctor who trained in Britain.

Until the uprising began, Assad cultivated an image as a youthful, modern leader in a region dominated by aging dictators. He was seen around Damascus with his glamorous wife, Asma -- the subject of a glowing profile in a recent edition of Vogue magazine -- and their three children.

The Syrian Embassy in London this week was forced to deny persistent rumors that Asma Assad has fled to Britain with the couple's young children.

Ambassador Sami Khiyami said in a statement that the rumors were "aimed at disrupting the delicate process of national reform taking place in Syria."