Ammon News - BEIRUT (Reuters) - U.N. Secretary-General Ban Ki-moon on Friday renewed his push for Syria to allow U.N. inspectors immediate access to investigate allegations that the government carried out a deadly chemical weapons attack on the outskirts of Damascus.

"I can think of no good reason why any party, either government or opposition forces - would decline this opportunity to get to the truth of the matter," the U.N. chief told a diplomatic forum in Seoul.

Syria's government has offered no public response to U.N. calls for its team to inspect the site of the attack, which opponents of Syrian President Bashar al-Assad said killed from 500 to well over 1,000 people.

They said more bodies were being found in the wake of Wednesday's mysterious pre-dawn killer fumes, which the Syrian government insists were not its doing.

The administration of U.S. President Barack Obama said it was "appalled" by the death reports.

A U.S. official familiar with initial intelligence assessments said the attack appeared to be the work of the Assad government. It was "the regime acting as a regime", the official said. But the Obama administration made clear that any response would await confirmation of a chemical attack and its origin.

Images, including some by freelance photographers supplied to Reuters, showed scores of bodies laid out on floors with no visible signs of injury. Some had foam at the nose and mouth.

French Foreign Minister Laurent Fabius said world powers must respond with force if allegations that Syria's government was responsible for the deadliest chemical attack on civilians in a quarter-century prove true. But Fabius stressed there was no question of sending in troops on the ground.

Talk of a forceful foreign response remains unlikely to be translated into rapid, concerted action given division between the West and Russia at Wednesday's U.N. Security Council meeting, and caution from Washington on Thursday.

Moscow has said rebels may have released gas to discredit Assad and urged him to agree to a U.N. inspection. On Wednesday, Russian objections to Western pressure on Syria saw the Security Council merely call in vague terms for "clarity" - a position increasingly frustrated Syrian rebels described as "shameful".

The State Department said senior U.S. and Russian diplomats would meet in The Hague next Wednesday to discuss ending Syria's civil war, in what would be the first such meeting since allegations of the chemical attack.

A senior State Department official said chemical weapons would also be discussed at the meeting. The meeting had previously been announced, but no date had been released.

Ban said he would send a top U.N. disarmament official, Angela Kane, to lobby the Syrian government in person and expected a swift, positive answer.

Obama has directed U.S. intelligence agencies to urgently help establish what caused the deaths, a State Department spokeswoman said while acknowledging it may be difficult given that the United States does not have diplomatic relations with Syria.

"At this time, right now, we are unable to conclusively determine CW (chemical weapons) use," the State Department's Jen Psaki told reporters. "We are doing everything possible in our power to nail down the facts," she added.

Another U.S. official said intelligence agencies were not given a deadline and would take the time needed to "reach a conclusion with confidence."

Former weapons investigators say every hour matters.

"The longer it takes, the easier it is for anybody who has used it to try to cover up," said Demetrius Perricos, who headed the U.N. team of weapons inspectors in Iraq in the 2000s.

'PEOPLE ARE GROWING DESPERATE'

Syria is one of just a handful of countries that are not parties to the international treaty that bans chemical weapons, and Western nations believe it has caches of undeclared mustard gas, sarin and VX nerve agents.

Syrian officials have called allegations against their forces "illogical and fabricated". They point to the timing of the attack, days after U.N. inspectors arrived after months of argument, and to previous assurances that, if they possessed chemical weapons, they would never use them against Syrians.

After months of negotiating with Assad's government to let inspectors into Syria, a U.N. team arrived in Damascus four days ago. Their task is to check on the presence, but not the sources, of chemical weapons that are alleged to have been released in three specific, small incidents several months ago.

Many rebels and activists in the opposition area say they have lost interest in promises of U.N. investigations or in help from abroad: "We are 7 km away, just a five-minute car ride from where they are staying," said activist Bara Abdelrahman.

"We're being exterminated with poison gas while they drink their coffee and sit inside their hotels."

Qassem Saadeddine, a commander and spokesman for the rebels' Supreme Military Council, said the group was still deliberating on how or if it should respond: "People are growing desperate as they watch another round of political statements and U.N. meetings without any hope of action," he told Reuters.

Syria's revolt against four decades of Assad family rule has turned into a brutal civil war that has killed more than 100,000 people in 2-1/2 years and divided the Middle East along largely sectarian lines.

Among world powers, the conflict has revived Cold War-era East-West tensions and on the ground the struggle has limped to a poisonous stalemate.

Assad's Alawite sect is an offshoot of Shi'ite Islam and has the backing of Iran and Lebanese militant group Hezbollah.

Western powers back the opposition but have been reluctant to fully commit to an Arab Sunni-backed revolt increasingly overtaken by Islamists linked to al Qaeda. Yet they have said the large-scale use of widely banned chemical weapons would be a game changer.

Syria's southern neighbor Israel, still technically at war with Damascus, said it believed Syrian forces had used chemical weapons and accused the world of turning a blind eye: "The world condemns, the world investigates, the world pays lip service," Strategic Affairs Minister Yuval Steinitz said.

In Paris, Fabius said that if the Security Council could not make a decision, one would have to be taken "in other ways", but he did not elaborate.

Immediate international action is likely to be limited.

European officials speaking on condition of anonymity said that options ranging from air strikes, creating a no-fly zone, or providing heavy weapons to some rebels were all still on the table - but that there was little prospect of concrete measures without U.S. backing, which still seemed unlikely.

"The American reaction following yesterday's attack was cautious," said one official. "And without U.S. firepower, there's little we can do."