Syria agreed to allow aid workers and supply convoys into four of its hardest-hit provinces, where at least 1 million people are in urgent need of aid because of injuries from the bloody civil conflict or the loss of homes and jobs, officials said Tuesday.

President Bashar Assad's government pledged in a written agreement to ease humanitarian access to the provinces even as the regime plunged itself into further international isolation by labeling a string of U.S. and European diplomats as unwelcome.

The deal requires Syria to provide visas to allow in an unspecified number of aid workers from nine UN agencies and seven other non-governmental organizations, and to cut through the bureaucratic red tape that has blocked convoys from delivering critically needed food, medicine and other supplies, said John Ging, operations director for the UN Office for the Coordination of Humanitarian Affairs.

But officials were quick to caution they will not declare success until the Assad regime delivers on its promises. Ging said he hopes it will be "days, not weeks" before the workers start filtering in and aid is delivered to the provinces of Daraa, Deir el-Zour, Homs and Idlib, and he urged Syria to keep up its end of the bargain.

"Whether this is a breakthrough or not will be evident in the coming days and weeks and it will be measured not in rhetoric, not in agreements, but in action on the ground," Ging told reporters after emerging from a closed-door session in Geneva to discuss the dire humanitarian situation in Syria.

Syria's uprising began with mostly peaceful protests, but a brutal government crackdown with tanks, machine-guns and snipers led many in the opposition to take up arms. The violence has grown increasingly chaotic in recent months, and it is difficult to assign blame for much of the bloodshed as the country spirals toward civil war.

Last week, Western nations expelled Syrian diplomats in a co-ordinated move over a massacre in which more than 100 people were slaughtered over one weekend in Houla, a cluster of small villages. The UN says pro-regime gunmen were believed to be responsible for at least some of the killings, but Assad has insisted his forces had nothing to do with it.

UN has struggled to deliver aid

On Tuesday, Syria barred a string of U.S. and European diplomats, saying they were "no longer welcome." The countries targeted by the expulsion order have already pulled their ambassadors from Damascus, but the move was symbolic of how far diplomatic ties have disintegrated over the course of the uprising that began last year in March.

Foreign Ministry spokesman Jihad Makdissi said Damascus has decided to take a "reciprocal measure" against ambassadors from the U.S., Britain, Turkey, Switzerland, France, Italy and Spain. A number of French, German, Canadian, Bulgarian and Belgian diplomats are also affected, Makdissi said.

Because of visa delays and hassles over customs clearances and how to distribute the supplies, the UN has struggled to deliver aid and it has largely trickled in through the Syrian Arab Red Crescent.

The UN launched the Syrian Humanitarian Forum, a gathering of diplomats to negotiate for access. "Today marks a step of progress, in that there is now an agreement with the Syrian government on the scale, scope and modality for a humanitarian response in Syria," said Ging after chairing its latest session, where he said Syria's representatives also expressed support for the new plan.

Ging said many in need in the four provinces have been injured during fighting or have lost jobs or homes. More than 78,000 Syrian refugees were also being helped in Iraq, Jordan, Lebanon and Turkey, the UN refugee agency said.

The Britain-based Syrian Observatory for Human Rights, which has a network of sources on the ground, said Tuesday that 113 soldiers have been killed in clashes with rebel forces across the country since Friday. The figure was impossible to confirm independently, but the Syrian government confirmed nearly 80 soldiers had been killed over the past three days.