Doctors Without Borders on Wednesday called on Syria's government to reverse its seven-year ban on the medical charity, issuing an urgent appeal for access to wounded people in regime-held territory.
Since Syria's conflict erupted in 2011, the medical charity known by its French initials MSF has been repeatedly denied permission to work in government zones, but has operated in opposition-held territory.
On Wednesday, it issued its first ever public appeal to Syria's government to reach those in need, regardless of location.
"Our actions are based on the needs of patients alone, not on the politics of war," said MSF general director Meinie Nicolai.
"We could begin working within days, if given authorisation, and could play a deeply beneficial role alongside other Syrian and international healthcare providers," she said.
The statement said MSF had submitted a request to Syria's foreign ministry in April but had not received a response.
"If our offer is again dismissed, we will continue to do what we can, where we can, because there are a great many people in great need of medical care in Syria today," said Nicolai
Syria's regime lost swathes of territory to rebels early in the uprising but has since made a comeback and recaptured large parts of the country.
In recent months, it has used military pressure and population transfers to flush fighters and civilians out of territory around Damascus, most notably the Eastern Ghouta suburb.
"The levels of trauma, both mental and physical, caused during the March offensive to take control of eastern Ghouta are beyond my comprehension," said Nicolai.
Hospitals backed by MSF in the rebel enclave treated more than 5,600 wounded in the first two weeks of the offensive alone.
"The number of affected people and the gravity of the needs mean that a significant and urgent medical response is required for these patients, regardless of who is in control of the territory," she added.
Prior to the assault, Ghouta's 400,000 residents had suffered five years of crippling regime siege that made food and medicine nearly impossible to access or afford.
The government has imposed sieges on opposition territory across Syria as a military tactic, restricting access for relief groups and even the United Nations.
But even when it recaptures a rebel zone and the siege ends, the Damascus government does not improve aid access, the UN said.
"The end of besiegement hasn't necessarily resulted in access for humanitarians," said the UN's regional humanitarian coordinator for Syria, Panos Moumtzis.
"From a humanitarian point of view, we're still frustrated about not being able to go in."
This year, UN aid had only reached a slim seven percent of two million Syrians in "hard-to-reach" areas, he said.
The UN has requested access tens of thousands of desperate people still living in Ghouta, but has been told by the government that it still is not safe.
"There shouldn't be any excuse for not going there," Moumtzis told journalists in Beirut last week.