The United Nations on Thursday defended its immediate response to Haiti's devastating earthquake after receiving criticism for being sluggish and uncoordinated.

"Senior leadership from the secretary-general on down were fully engaged right form the start, right from the very beginning, " said UN spokesperson Martin Nesirky.

"They worked nonstop to make sure aid was coordinated, work with troop-contributing countries is continuing, and a Security Council resolution went through in record time."

During the first few days after the earthquake hit on Jan.12, tough logistics made it difficult for the United Nations to deliver emergency aid. Blocked roads and a small airport tested the world body in its ability to coordinate a massive humanitarian operation, even as its own staff suffered majored loses.

But as frustrations grew and isolated reports of violence and looting began to seep out to the word, questions began to arise over the effectiveness of the UN's response.

A blog on Foreign Policy magazine, a division of the Washington Post, questioned whether the earthquake was UN Secretary-general Ban Ki-moon's Katrina, a reference to the former U.S. administration's incompetent handling of the Category Five hurricane that hit Louisiana in 2005.

"This is one person's report," retorted Nesirky. "It is entirely up to every journalist to write what they see fit."

In response to several questions about the immediate hours after the earthquake struck just before 4 p.m. EST, Nesirky gave a detailed account describing a UN operating at overdrive.

Ban was on his way back to New York from a regional retreat when he was informed about the 7.3-magnitude earthquake. Upon arriving at his residence, Ban immediately ordered his advisors to activate the crisis management group that deals with massive disasters, said Nesirky.

Meanwhile, the Department of Peacekeeping Operations (DPKO) organized a meeting with senior advisors in the Situation Center, which "lasted throughout the night."

"The key priority was to reach the mission (in Haiti) to find out what was happening and to contact them," said Nesirky.

Communication lines in Haiti were down and the UN headquarters based at the Christopher Hotel in Port-au-Prince had completely collapsed.

Ban's first phone call was to U.S. Ambassador to the UN Susan Rice, at which time he requested humanitarian support from the U.S. government. This was the "correct conduit to launch such an appeal, " said Nesirky, who noted that Ban also called special envoy Bill Clinton.

Several statements were issued, said Nesirky, including one by the DPKO which outlined a description of the severe damage to the UN headquarters and its staff.

On Wednesday morning, as daylight broke in Haiti and it was easier to get a visual assessment of the damage, the secretary- general met with key staff members. It was then that the UN decided Edmond Mulet would take charge of the UN Mission in Haiti as the fate of Hedi Annabi was still unknown.

After the meeting, Ban came to the Security Council stakeout just after 8 a.m. EST to inform reporters about the UN's response and make it "clear that this was a major catastrophic earthquake," said Nesirky.