Updated

Syrian rebels sent a wave of rockets slamming into regime strongholds in the central city of Homs Thursday, triggering a succession of massive explosions in a weapons depot that killed at least 40 people and wounded at least 120, an opposition group and residents said, hours after President Bashar Assad vowed that his troops will win the war.

The rocket attack sent a massive ball of fire and a black mushroom cloud into the sky and caused widespread damage and panic among residents, many of whom are supporters of Assad. Firefighters struggled for two hours to put out the flames.

"The first explosion knocked people off their feet," said one Homs resident, adding that successive smaller explosions lasted for over an hour. He declined to be named, fearing retaliation.

Activists in the city corroborated an account from the Britain-based Syrian Observatory for Human Rights, saying at least 40 were killed and many others wounded. They said the regime is known to keep arms depots in those areas.

An official at the governor's office in Homs said six people were killed and 145 wounded when about 10 rockets slammed into the neighborhood of Zahra and the nearby sports stadium. He said one rocket struck a civil defense center, referring to the Wadi Dahab area, although he did not directly address the weapons depot.

He spoke on condition of anonymity because he wasn't authorized to release the information.

Earlier in the day, Assad praised his troops while he made his first known public trip outside the capital since last March.

Syrian state-run TV said Assad had visited Daraya to inspect his troops for the country's Army Day. The last time he was outside his seat of power, Damascus, was in March 2012, according to the Associated Press.

The station did not provide details, but the presidency's Facebook page released a photo of Assad in a blue suit and tie chatting with two soldiers before what appears to be a damaged building.

Daraya, just south of Damascus, was held by rebels for a long time and it took the army weeks of heavy fighting to regain control earlier this year.

"The achievements on the ground speak for themselves," Assad told soldiers in Daraya, a few miles south of the capital.  "Without you we would all be slaves to the countries that want to subjugate us. But the Syrian people will never be slaves. Not in the past, present or future," he said.

In a statement marking Army Day, Assad said his men are confronting the "fiercest barbaric war in modern history."

"Had we in Syria not been confident of victory, we wouldn't have been able to resist" for more than two years, Assad said in a statement carried by the state news agency SANA.

Assad's comments followed several significant regime gains against the rebels on key battlefields recently, mostly in the central province of Homs and Damascus, and a economic boost from Iran Wednesday in the form of a $3.6 billion credit to buy oil products, officials and bankers told Reuters.

The rebels suffered two major setbacks during a wide-ranging government offensive in central Syria. In June, Assad's army recaptured the strategic town of Qusair near the Lebanese border, and this week, government troops took control of a district in the city of Homs that had long been an opposition stronghold.

Five major aid agencies also warned on Thursday that the Syrian refugee crisis is stretching aid efforts to their limits.

The agencies — including CARE International, Oxfam, Danish Refugee Council, Handicap International and World Vision — said they are increasingly concerned that the international response is failing to match the scale of the crisis.

Their joint statement said more than 1.4 million Syrians — or 80 percent of all Syrian refugees — are now living in tents, temporary settlements, or overcrowded and expensive rented accommodations.

"People are living in shopping centers, empty garages or makeshift tents on derelict land," said Oxfam's response manager in charge of Syria, Colette Fearon. "They are struggling to survive on little or nothing, and many are falling through the cracks with no immediate end in sight to the conflict the problem will only get worse."

"We need to make sure assistance reaches refugees no matter where they are," she added.

More than 100,000 people have been killed since the uprising against the Assad family's four-decade rule began in March 2011. The revolt later escalated into a civil war, which has uprooted millions of people from their homes.

Last month, assistant U.N. secretary-general for human rights, Ivan Simonovic, said an estimated 5,000 Syrians are dying every month in the country's civil war and refugees are fleeing at a rate not seen since the 1994 Rwanda genocide.

Because of the huge numbers of people fleeing the conflict, refugees are pursuing whatever options they can to find shelter, the aid groups' statement said.

Many arrive in shelters across the border with just the clothes on their backs and need help to cover basic costs such as food, safe drinking water and a roof over their heads, it added.

Health care has become a luxury that many refugees cannot afford, and vulnerable groups, such as the elderly and persons with disabilities or chronic disease, have no access to essential services beyond what organizations such as Handicap International can provide.

"People left Syria with nothing and are trying to carve out a new life for themselves," said Hugh Fenton of the Danish Refugee Council. "But they are starting from scratch and everything is expensive. Many are getting into increasing debt in order to survive."

The Associated Press contributed to this report.