Free Syrian Army fighters man a checkpoint in Raqqa province, eastern Syria April 15, 2013. (Reuters)

Syrian rebels and activists reacted with resigned bitterness Friday to assertions that the Syrian government has used chemical weapons, underscoring their low expectations of action by the United States and other Western countries after more than two years of conflict.

Britain and France said Thursday they have credible evidence that Syria has employed nerve agents within its borders more than once since December. In letters to U.N. Secretary General Ban Ki-moon this week, the two governments said soil samples and interviews with witnesses and opposition sources supported claims that President Bashar al-Assad’s forces had used the chemical weapons in and around the cities of Aleppo, Homs and possibly the capital, Damascus.

The European reports constitute the first official outside allegations of the use of chemical weapons in a conflict that has left more than 70,000 dead and nearly a quarter of the population displaced, according to U.N. figures.

But rebel fighters and activists quickly dismissed the reports as unlikely to affect the daily reality of civilians and fighters in Syria, where dozens of people are killed every day and major cities have been reduced to devastated landscapes of torn concrete and twisted metal.

“The rebels on the ground have stopped paying any attention to any investigation, meetings or statement by any Western countries regarding the Syrian revolution,” Mohamed Nahal, an activist based in Damascus who was reached by Skype, said Friday. The world has watched Assad batter Syria’s cities and towns with airstrikes, rockets, tank shells and Scud missiles for more than two years “without doing anything for the rebels so far,” he said.

Interactive Grid: Keeping track of the conflict in Syria through videos, images and tweets.

Even so, the prospect of chemical-weapons use poses a difficult test for the Obama administration, which has so far declined to arm Syria’s disparate rebel forces but has also called chemical weapons “a game-changer.”

Some fighters expressed muted hope Friday that the reports could prompt a serious international response.

“We are hoping now that both Western and Arab governments will help us,” said Abo Huda Alhomsi, a member of the Free Syrian Army in Homs, near the Lebanese border.

“But the problem is that they think we are Islamic extremists who will be killing minorities,” he said, citing Syrian government claims. “This is not true,” he added, but he said the rumors had hindered badly needed aid to the rebels.

Washington has resisted sending any significant nonlethal military aid to Syria’s rebels, for fear it would fall into the hands of the extremist contingents that are increasingly taking the lead in many frontline battles.

In December, the administration labeled one of Syria’s rebel groups, Jabhat al-Nusra, or the al-Nusra Front, a terrorist organization. Group leaders have since publicly sworn their allegiance to al-Qaeda leader Ayman al-Zawahiri.

Salman Shaikh, director of the Brookings Doha Center, echoed activists’ predictions Friday that the chemical-weapons reports will be unlikely to spur direct U.S. involvement in the conflict.

“I don’t see any great resolve to intervene. If the use continues or expands, the only time I see it becoming a real alarm is when they start to see these weapons getting out of the regime’s control,” Shaikh said. For now, Syrian officials are probably “experimenting” — testing the so-called red lines, he said.

No one in the international community wants to “own” Syria’s conflict, Shaikh said, noting that no country has been willing to intervene on behalf of the country’s beleaguered population in previous instances of government airstrikes or massacres. “And therein lies the problem,” he said.

The Syrian government and rebel forces have traded accusations of chemical-weapons use in recent months. The European reports appeared intended, in part, to counter government allegations that the rebels used such weapons in a March attack near Aleppo in which 26 people, including regime troops, were killed.

The Syrian government has not publicly acknowledged the European assertions.

In other developments Friday, the Syrian government and Syrian activists said that Ali Ballan, the Social Affairs Ministry’s public relations chief, had been gunned down the night before as he sat in a restaurant in Damascus.

Activists also reported heavy fighting near the town of Qusair, close to the Lebanese border, and shelling on the eastern outskirts of Homs that killed 18 people. The Syrian state news agency reported that government forces continued to destroy “terrorist cells” around the capital.

“We are afraid of Assad using more chemical weapons,” Alhomsi said. FSA fighters in the countryside around Damascus have received “warnings,” he said, “that if the FSA doesn’t pull back, he will use chemical weapons.”

Ahmed Ramadan and Suzan Haidamous in Beirut, Colum Lynch at the United Nations and Karen DeYoung in Washington contributed to this report.