He added that only about $180m of the $690m required for a three-year recovery plan had been received.
Nargis caused widespread devastation in Myanmar's Irrawady Delta region and parts of the former capital, Yangon.
Two years later the UN said recent assessments had shown 100,000 families still need to rebuild their homes, 180,000 people face acute water shortages and agricultural support and community job opportunities are needed.
A UN statement appealed for the international community to support the Nargis recovery plan and recognise that cyclone recovery was a long-term process.
According to Parajuli, assistance from some sources – including Australia, the UK, US and European Union – had increased, but a number of other donors scaled back their commitment after the initial relief period.
The plan was developed last year by a body that includes representatives of Myanmar's government, UN agencies and the 10-member Association of Southeast Asian Nations (Asean).
Parajuli also urged Myanmar's military government to support humanitarian agencies' efforts, particularly with respect to providing visas and access to the delta for all aid workers.
Aid efforts restricted
|The Myanmar government was criticised for its slow response to the disaster [EPA]
However, according to the New York-based Human Rights Watch (HRW), the military government of Myanmar continues to hinder efforts in providing humanitarian aid to the survivors.
Twenty-two local aid workers are currently being detained while restrictions on travel are further hampering efforts to deliver much-needed assistance, HRW said in a report marking the anniversary of the disaster.
"Two years after one of the world's worst natural disasters, local aid workers still feel the brunt of continued repression by the military authorities," said Elaine Pearson, the group's deputy Asia director.
Officials are slow to issue travel permits required to transport aid, while the state is taking a more central role in running humanitarian operations, fanning fears of manipulation, the report said.
It added that humanitarian access to the country was again narrowing as the military government steps up preparations for widely-criticised national elections, expected to be held later this year.
Myanmar's military rulers faced a storm of international criticism over its slow response to Cyclone Nargis.
A deal struck between the international community and the Myanmar government led to an opening up of aid channels, but hopes that could lead to greater access in the future were never realised, HRW said.