The newly elected head of Syria's opposition briefed European foreign ministers Monday on the crisis there, European Union foreign affairs representative Catherine Ashton said.

Ashton met Monday with Ahmed Moaz al-Khatib and pledged European support ahead of the monthly meeting of European Union foreign ministers.

"We want to help, but it's their country," she said.

Al-Khatib was to discuss his proposal for a political transition to end the hostilities that have left thousands of people dead during nearly 21 months of violence that Syrian President Bashar al-Assad has characterized as a fight against terrorism.

Ashton said the world must take a stand against al-Assad's actions.

"It is important that we recognize the terrible things that have been happening in Syria and the responsibility that Assad has," Ashton said. "We said from the very beginning that it is no place to be in a position of power in your country if you respond to peaceful demonstrations with the murder of your citizens."

After hearing from al-Khatib, the foreign ministers released a statement saying, "The EU is seriously concerned about the potential use and transfer of chemical weapons in Syria and reminds the Syrian regime and other parties that, in case of their use, those responsible will be held accountable."

Syria has accused the United States of working to falsely accuse the country of using chemical weapons, Syrian state-run media said Monday.

"The U.S. administration has consistently worked over the past year to launch a campaign of allegations on the possibility that Syria could use chemical weapons during the current crisis," the Foreign Ministry wrote in letters to U.N. Secretary-General Ban Ki-moon, the state-run Syrian Arab News Agency reported.

"What raises concerns about this news circulated by the media is our serious fear that some of the countries backing terrorism and terrorists might provide the armed terrorist groups with chemical weapons and claim that it was the Syrian government that used the weapons," SANA quoted the letters as saying.

U.S. officials have said they have seen intelligence suggesting that Syrian military units may be preparing chemical weapons for use.

President Barack Obama has said any use of chemical weapons would cross a "red line," eliciting swift U.S. reaction.

The United States and European allies are using defense contractors to train Syrian rebels to secure chemical weapons stockpiles, a senior U.S. official and several senior diplomats said.

The training, in Jordan and Turkey, covers the monitoring and securing of stockpiles of weapons and materials, said the officials, who spoke on condition of anonymity because they were not authorized to publicly discuss the issue.

Some contractors are working with rebels in Syria to monitor sites, one of the officials said.

Opposition groups said fighting continued Monday across the country.

At least 142 people died Monday, 59 of them in Aleppo and 50 in Damascus and its suburbs, the Local Coordination Committees of Syria said.

In one Aleppo neighborhood, opposition activists said, they discovered 10 handcuffed and blindfolded corpses killed by government forces in recent weeks, the Syrian Observatory for Human Rights reported.

CNN is unable to confirm casualty reports as the government has severely restricted access by international journalists.

The Observatory said a rebel group seized control of a government military base in northwest Syria.