The United Nations is launching its biggest humanitarian appeal ever, seeking $5.2 billion to fund relief operations for Syria until the end of the year.

The figure presented at an international conference in Geneva on Friday is a sharp increase from the $3 billion the global body had previously estimated it would need this year.

Officials say the calculation is based on the worsening security situation inside Syria, the sharp increase in people fleeing to neighboring countries, and the assumption that the conflict won't end soon.

U.N. aid agencies and independent relief organizations are asking for $2.98 billion to help refugees in Jordan, Lebanon, Turkey, Iraq and Egypt. They are also requesting $1.4 billion to pay for aid operations inside Syria. The Jordanian and Lebanese governments are seeking $830 million.