BEIRUT (AP) With the world's attention on Syria's chemical weapons stockpile, international aid organizations and opposition groups are warning of widespread food shortages across the country.

Save the Children said in an appeal released Monday that more than 2 million Syrian children could not obtain enough food, and activists told The Associated Press that six people have died of starvation in the suburbs of Damascus in the past days, including an 18-month old baby.

Thousands of people are believed trapped in suburbs east and west of the capital Damascus held for months now by rebels fighting to topple President Bashar Assad. Regime troops are besieging the areas, and residents say food is increasingly difficult to find. Rebels say they are trying to break the blockade.

The suburbs, a major battlefront in Syria's civil war, were the site of the Aug. 21 attack that a U.N. report found included the use of the nerve agent sarin. They were home to more than 2 million people before the war, but it is unclear how many are there now.

On Monday, the opposition Syrian National Coalition accused government forces of tightening their months-long siege. "Assad's forces are starving people to death in those areas," the coalition claimed. "Famine looms in the horizon."

In violence in the capital on Tuesday, a car bomb exploded in a Damascus neighborhood, killing at least three people, the government and activists said.

State-run SANA news agency said the blast hit the contested district of Tadamon, which has seen months of fighting between the military and rebels seeking to topple President Bashar Assad. It said 11 others were wounded.

The Britain-based Syrian Observatory for Human Rights said at least seven people were killed and 15 were wounded. The difference in the death tolls could not immediately be reconciled.

There was no immediate claim of responsibility for the attack, which comes amid raging battles between troops and rebels in several parts of the country. Extremist factions among the rebels have in the past carried out suicide and car bombings.

In its appeal, Save the Children cited reports that one in 20 children in suburbs of Damascus is severely malnourished.

It said that more than four million Syrians more than two million of them children cannot produce or buy enough food. Food shortages are compounded by an explosion in prices of basic staples, the group said.

"The world has stood and watched as the children of Syria have been shot, shelled and traumatized by the horror of war," said Roger Hearn, Save the Children's regional director for the Middle East. "The conflict has already left thousands of children dead, and is now threatening their means of staying alive."

The United States and Russia brokered an agreement for Syria to give up its chemical weapons but U.N. diplomats say they are at odds on details of a Security Council resolution spelling out how it should be done and the possible consequences if Syria doesn't comply.

The United Nations said the team of chemical weapons inspectors led by Swedish expert Ake Sellstrom will return to Syria on Wednesday.

U.N. officials said Sellstrom's team will return to complete its investigation into "pending credible allegations" of chemical weapons use in the civil-war struck Arab state.

In the statement Tuesday, the U.N. said the investigation will include gathering evidence from an alleged chemical weapons attack on March 19 on the village of Khan al Assal outside the city of Aleppo, which was captured by the rebels in July.

On its previous trip to the country, the team compiled a report that said nerve agent sarin was used in an Aug. 21 attack near Damascus. The U.S. and its allies say Assad's regime was behind the attack, which according to Washington killed 1,400 people. Activist groups say the death toll was significantly lower, but still in the hundreds.

Damascus blames the rebels for the attack, and Russia, a close ally of Assad, said the U.N. report does not provide enough evidence to blame the Syrian government. It has also demanded that U.N. inspectors probe other attacks that allegedly included chemical agents.

"We are pleased that our call for U.N. inspectors to return to Syria to investigate other episodes has brought results," Ryabkov told the Russian parliament Tuesday, according to state news agency RIA Novosti. He did not elaborate.

At the U.N., the head of the organization's World Food Program demanded Monday that a potential cease-fire agreement include access for aid workers.

Ertharin Cousin told The Associated Press that an agreement, which will be discussed at the start of the annual U.N. General Assembly on Tuesday, envisions a cessation of hostilities so chemical experts trying to bring Syria's stockpile under international control can travel across the country, including to many conflict areas where WFP and other humanitarian workers have been unable to bring in desperately needed aid.

WFP is currently feeding 3 million people inside Syria and 1.2 million in neighboring countries. Cousin said the goal is to step up supplies so that 4 million internally displaced people and 1.5 million refugees are getting food by the end of October.