Aug. 3 (Bloomberg) -- Fighting intensified between Syrian forces loyal to President Bashar al-Assad and rebels in Damascus suburbs a day after United Nations special envoy Kofi Annan abandoned his effort to mediate a cease-fire.

Clashes broke out today in the Damascus suburb of Jdeidet Artouz and near the Marj As Sultan military airport east of the capital, the opposition Syrian Observatory for Human Rights said. The Syrian News Agency said a “terrorist armed gang” fired mortars on the Yarmouk neighborhood, killing and wounding many civilians. A man died in a helicopter attack in Aleppo, the nation’s commercial hub, the observatory said.

Annan’s departure after less than six months is a blow to international efforts to broker a diplomatic solution to the increasingly violent conflict. What began in March last year as a largely peaceful protest movement has become a civil war.

Annan blamed both sides for the increasing militarization of the conflict and said a “clear lack of unity” in the UN Security Council -- where Russia has used its veto three times to protect the Assad government -- “fundamentally changed” his ability to be effective. His resignation as the special envoy appointed by the UN and Arab League is effective Aug. 31, and talks are under way to find his successor.

U.K. Foreign Secretary William Hague today called Annan’s resignation “a bleak moment” for efforts to find a diplomatic solution to the Syrian conflict and said Britain will step up its support for rebels without sending arms.

“We are helping elements of the Syrian opposition but in a practical and non-lethal way,” he told BBC Radio 4’s “Today” program.

Lacking Tools

U.S. Secretary of State Hillary Clinton said Annan “worked tirelessly to try to build consensus in the international community, end the bloodshed, and usher in a government that would meet the legitimate aspirations of the Syrian people,” according to a statement. “Unfortunately, the Security Council was blocked from giving him key tools to advance his efforts.”

Syria expressed “regret” over the news of Annan’s resignation, state-run news agency SANA said. Citing a Foreign Ministry statement, SANA said Syria had always expressed its “full commitment” to Annan’s plan and accused unnamed countries of obstructing his mission by “supporting and harboring the armed terrorist groups leading to the continuation of violence in the country.”

Russia Blamed

Hours after Annan’s announcement, Western powers blamed Russia for the failure of the peace efforts.

The “highly regrettable” and “very unfortunate” vetoes “place both Russia and China on the wrong side of history and on the wrong side of the Syrian people,” White House press secretary Jay Carney told reporters on board Air Force One en route to Florida.

In Geneva, Annan expressed his own frustrations.

He said that, while some had labeled his job as a “mission impossible,” the “clear lack of unity in the Security Council” compounded the difficulties he already faced because of both “Syrian government intransigence” and the “escalating military campaign of the opposition.”

Annan’s action “reflects the reality that the center of gravity in this crisis lies on the ground within Syria, and international diplomacy has become largely irrelevant,” Robert Danin, a senior fellow at the Council on Foreign Relations in New York, said by telephone. “Annan was dealt a very weak hand and had very few cards to play.”

Dozens Killed

With the UN powerless to act, the survival of the four- decade Assad dynasty will probably be decided on Syria’s streets. Aleppo, the country’s most populous city, is shaping up as the biggest test yet of opposition fighters’ capabilities against artillery and air power, with thousands of civilians slipping across increasingly porous borders to seek refuge.

At least 133 civilians died across the country yesterday, the Syrian Observatory said today. It said 26 people were killed in Deraa, while another 13, including three children, died during shelling in suburbs of Damascus.

The 22-member Arab League, which suspended Syria last year, is trying to keep diplomacy alive at the UN by calling a vote today on a largely symbolic resolution “expressing grave concern about Syrian authorities’ threat to use chemical or biological weapons.”

Passages in the text demanding that Assad step down and calling on states to apply economic sanctions were removed in a bid to gain more than 100 votes in the 193-member assembly.

‘One-Sided, Unbalanced’

Russia, which sells arms to Syria, won’t back the resolution because it’s “one-sided and unbalanced,” the Foreign Ministry said in a statement yesterday.

During a meeting with Vladimir Putin yesterday, U.K. Prime Minister David Cameron failed to get the Russian president to change his mind on backing tougher measures to hold Assad accountable, according to a Security Council diplomat who asked for anonymity because diplomatic talks are private.

“Of course there have been some differences in the positions we’ve taken over the Syrian conflict,” Cameron told reporters after the meeting at his Downing Street office. “We both want to see an end to that conflict and a stable Syria, and we’ll continue to discuss, with our foreign ministers, how we can take this agenda forward.”

As for Annan, Putin expressed regret at his departure and said the former UN secretary-general is “a very decent man and brilliant diplomat,” according to comments reported by Interfax.