The International Committee of the Red Cross (ICRC) is appealing for an extra $27m (£17m) to fund its operation in Syria until the end of this year.
The ICRC, the only international aid agency working inside Syria, says hundreds of thousands of people remain in need.
Despite the ceasefire which came into force last month, the humanitarian needs remain enormous, it says.
In the latest violence, activists said two civilians died in Idlib province.
While some parts of Syria have seen intermittent periods of calm, in many other areas, there has been no let-up in the violence, the ICRC says.
On Sunday, activists said troops had killed three people in the eastern province of Deir al-Zour. There was also reportedly fighting in Hama and Idlib provinces.
The ICRC says gaining unrestricted access to conflict areas is a top priority. It hopes to provide food for 100,000 people, supply basic household items for 25,000, and to restore public services such as water and electricity to 1.5 million.
But the agreement of the Syrian authorities will be needed too, it says, adding it is encouraged by recent discussions with both government and opposition forces.
Life for aid workers in Syria remains very risky: the head of the Syrian Arab Red Crescent and two Red Crescent volunteers have already been killed in the conflict, says the BBC’s Imogen Foulkes in Geneva.
On Sunday, parliamentary elections, promised last year by President Bashar al-Assad, were held – the first in 40 years not to guarantee a majority for the ruling Baath Party. Opposition groups dismissed them as a sham, calling for a boycott.