Syria has granted international relief workers access to four key sites after agreeing to a $180-million plan to help one million needy people, the United Nations said on Tuesday.
The UN Office for the Coordination of Humanitarian Affairs (OCHA) said planning teams were deployed on Sunday to Homs, Idlib, Daraa and Deir Ezzor.
Aid workers will work alongside the Syrian Arab Red Crescent to deliver supplies including food and medicine, said John Ging, director of OCHA's coordination and response unit.
Damascus has also agreed to allow more local and international non-governmental organisations (NGOs) to deliver aid, said Ging following a meeting in Geneva to discuss scaling up the humanitarian response.
The Humanitarian Forum on Syria, the third gathering of its kind, was hosted by OCHA, the Arab League, the Organization of Islamic Cooperation, and the European Commission Humanitarian Office (ECHO).
The agencies want to increase the capacity of aid workers and speed up the process, which is being stalled by the wait for visas and convoy clearance.
"We don't have a lot of time because I have a feeling we are running behind an accelerating humanitarian crisis," said Claus Sorensen, head of ECHO.
The UN estimates that at least one million people are in need of assistance inside Syria after 15 months of violence.
Relief agencies are also attempting to help the more than 78,000 Syrians who are living as refugees in neighbouring countries.
Ging said that following intense negotiations the Syrian government had agreed to a $180-million (145-million-euro) draft aid plan.
Signup to our newsletter and follow us on Facebook and Twitter!
"The proof of their good faith in terms of that agreement will be in the action of the coming days," he said.
The World Food Programme (WFP)is upping its assistance and will now provide food for 500,000 people.
Tens of thousands are also receiving medical help from the World Health Organization (WHO) and the International Committee of the Red Cross (ICRC).
Household kits including kitchen equipment and bedding are meanwhile being delivered to about 50,000 people.
"They (the Syrian authorities) have agreed on expanding the presence of UN humanitarian agencies in a number of key areas where we will be able to better coordinate, facilitate, monitor and report on the humanitarian effort," said Ging.
"Whether it's a breakthrough or not will depend on the action on the ground."
Of the $180 million sought, 20 percent has been received so far.
Thirty-six percent of a separate $84 million refugee response plan has meanwhile been met.
Ging said that countries previously reluctant to give their cash would be spurred by the signing of the agreement.
The US announced Tuesday it would boost its aid by $12.8 million, taking the sum it has committed this year to more than $52 million.
Deputy Assistant Kelly Clements from the Bureau of Population, Refugees and Migration told reporters in Geneva she was "cautiously optimistic" about the agreement reached with Damascus.