Syrian Foreign Minister Walid Muallem has said he rejects "utterly and completely" that Syrian government forces used chemical weapons.
He was speaking in Damascus after the US said there was "undeniable" proof of a chemical attack.
He said UN weapons inspectors had been unable to go to a second site because rebels could not ensure their safety.
The US and its allies are considering launching strikes on Syria in response to deadly attacks last week.
The UN has confirmed its inspection team has delayed its second trip to the Damascus suburbs by one day for safety reasons.
Meanwhile, UK Prime Minister David Cameron said the British Parliament would be recalled early to discuss the country's response to last week's suspected chemical weapons attacks in Syria. British MPs will meet on Thursday.
The UK is making contingency plans for military action in Syria, with UK PM David Cameron cutting short his holiday and returning to London to deal with the Syrian crisis.
In Damascus, Mr Muallem told a news conference that if a military act was carried out against Syria, the pretext of chemical weapons would be false, baseless and groundless.
"They said the Syrian forces were the ones who carried out this attack. I deny this utterly and completely to [US Secretary of State John] Kerry," he said.
"There is no country in the world that uses a weapon of ultimate destruction against its own people."
The Syrian foreign minister also insisted the government was honouring all the pledges it made to the UN over access and protection for the inspectors.
On Monday, the UN inspectors said they had come under sniper fire as they tried to visit an area west of the city.
Meanwhile, Russia and China have stepped up their warnings against military intervention in Syria, with Moscow saying any such action would have "catastrophic consequences" for the region.
Russian foreign ministry spokesman Alexander Lukashevich has called on the international community to show "prudence" over the crisis and observe international law.
Late on Monday, the US said it was postponing a meeting on Syria with Russian diplomats, citing "ongoing consultations" about alleged use of chemical weapons in Syria.
Hours later, Russia expressed regret about the decision. The two sides had been due to meet in The Hague on Wednesday to discuss setting up an international conference on finding a political solution to the crisis.
The Russian deputy defence minister, Gennady Gatilov said working out the political parameters for a resolution on Syria would be especially useful, with the threat of force hanging over the country.
On Monday, Mr Cameron spoke to Russian President Vladimir Putin who said there was no evidence yet that Syria had used chemical weapons against rebels, Mr Cameron's office said.
The official Chinese news agency, Xinhua, said Western powers were rushing to conclusions about who may have used chemical weapons in Syria before UN inspectors had completed their investigation.
Both the Syrian government and rebels have blamed each other for last Wednesday's attacks.
Medical charity Medecins Sans Frontieres said three hospitals it supported in the Damascus area had treated about 3,600 patients with "neurotoxic symptoms", of whom 355 had died.
US officials said there was "little doubt" that President Bashar al-Assad's government was to blame.
The UN Security Council is divided, with Russia and China opposing military intervention and the UK and France warning that the UN could be bypassed if there was "great humanitarian need".
The UN says more than 100,000 people have been killed since the uprising against President Assad began more than two years ago. The conflict has produced more than 1.7 million registered refugees.