Persistent violence has made it difficult for the only international aid agency in Syria to access the country's neediest areas.

Heavy shelling killed at least 16 people in the flashpoint city of Homs Tuesday as the Red Cross continued to press for a ceasefire to allow food and supplies in.

The agency is trying to broker the deal at a time when troops loyal to President Bashar Assad are bolstering efforts against rebel forces and military defectors. Homs and the nearby Baba Amr district have become a central staging area for these clashes.

Spokesperson Bijan Farnoudi said the International Committee of the Red Cross (ICRC) has managed to get into Homs about 25 times in recent months.

"That's not sufficient," he told CTV's Canada AM on Tuesday. "There are many more areas…that are very much affected as well."

The ICRC says it is trying to negotiate a ceasefire among Syrian opposition and rebel forces with the assistance of the Syrian Arab Red Crescent.

"In areas where the need is most dire, those are the same areas that we have the biggest trouble getting to," he said in a phone interview from Geneva.

Farnoudi said a brief cessation of fighting would allow humanitarian workers to fan into needy areas delivering food and providing health services. He noted that the Syrians in need of aid aren't just those who were injured in combat.

"It's your everyday person; someone who suffers from appendicitis, or a broken leg or a pregnant woman," he said.

The United Nations has said that 5,400 were killed in the Syrian conflict in 2011 alone. Activists estimate hundreds more have died in 2012. Those estimates also exclude the deaths of ordinary citizens affected by conflict, but not killed in combat.

Clashes between government troops and rebel forces have stretched on for about 11 months now and it's become next to impossible to verify a death toll. Most news outlets and humanitarian organizations aren't allowed to enter the country.

Farnoudi said a tight rein on information and culture of fear is preventing Syrians from seeking out medical help when they need it. He said some in high-conflict areas are too afraid to travel to a hospital or are wary of what might happen when they get there.

"There's no guarantee that the clinic or the hospital is actually a safe place where a patient is just a patient and not someone who may be suspected of being on one side or another side," he said.

The presence of aid workers is reportedly decreasing as well. According to Farnoudi, the Syrian Arab Red Crescent has lost staff in recent months due to work in increasingly dangerous conditions.

Abdulrazak Jbero, head of the Red Crescent's Idlib branch, was shot to death on Jan. 25 while travelling in a car from Damascus back to the town. Further details are unclear.

Meanwhile, investigators with the United Nations are asking Syria to free at least 16 activists, bloggers and journalists arrested by authorities last week.

Fears abound that the detainees, including U.S.-born blogger Razan Ghazzawi and activist Mazen Darwish, will be tortured. Reports indicate they were taken to a detention centre run by Syria's military intelligence near Damascus.

While rival troops continue attacks in Baba Amr, a possible resolution to the conflict is unclear. Russia and China have vetoed two UN Security Council resolutions aimed at changing the situation on the ground.

In a statement issued in early February, the ICRC's Syrian delegation head said it's ordinary Syrians who are most affected by the conflict.

"The population, particularly the wounded and sick, are bearing the brunt of the violence," wrote Marianne Gasser.

The ICRC and Red Crescent reported on Feb. 12 that a convoy loaded with food, medical supplies, blankets and other supplies reached Homs. A similar one arrived in the town of Bludan around the same time.