The United Nations' humanitarian chief Valerie Amos has told Sky News that as many as 2.5 million people need humanitarian help in Syria.
The Baroness added aid organisations in the country are working to capacity and a political solution and a cessation in the fighting is needed to end the crisis.
She said: "When I was here in March I spoke to authorities about the importance of the humanitarian situation. They have now accepted that, they have a response plan but we now have to revise that plan.
"We thought it was 1.2 million people that needed help then. We think that figure might now be has high as 2.5 million."
More money and support was required and those engaged in the fighting needed to be reminded that it is civilians who are bearing the brunt of the violence, she said.
A man cries in front of houses destroyed by the Syrian army in Azaz "We need people, we need money. We made an appeal at the end of March but we only have 40% of the money. People are tired, they want to go back home. But the crucial thing to make a difference is a stop to the fighting.
"I can't make that happen. But I can encourage those engaged in the violence to remember that it is ordinary women and children who are suffering the brunt of this."
Sky's Foreign Affairs Editor Tim Marshall said the Syrian President Bashar al Assad's regime was concerned international aid would not be used effectively.
He said: "Baroness Amos is here on the diplomatic side of trying to get aid in, and on that she hasn't fully succeeded.
"What she came here to do was to persuade the government to open up the roads and let the huge UN aid convoys in, and all the big aid agencies of the world like Oxfam and Christian Aid.
"But the government has said, 'No, we're not going to do that because we think a lot of the aid will fall into the hands of the rebels.'"
A Free Syrian Army fighter fires an AK-47 rifle in Aleppo The Baroness has been holding talks in Syria to raise awareness about the worsening humanitarian situation and to gain access to civilians caught up in the fighting.
She visited a school in the Zahera district of south Damascus where hundreds of civilians who have fled the fighting were living without proper food, bedding or running water.
The UN Security council was to meet later to end the observer mission to Syria following a day of violence across the country.
A bomb exploded in the Syrian capital on Wednesday near several government buildings and the UN's hotel, wounding three people.
Mr Assad's forces still have control of Damascus, but fierce fighting is continuing in the northern district of Aleppo where they have been trying to dislodge resistance from the rebel opposition.
Government air strikes in the nearby city of Azaz killed 30 people on Wednesday, according to activists.
