Roughly 400 United Nations police and military troops have been brought into Haiti's capital from around the country amid concerns that security could deteriorate further, the UN chief of peacekeeping operations said Monday.

For the time being, security remains under control in the quake-ravished nation, Alain LeRoy told reporters, but there have been "sporadic incidents" due to Haitians becoming frustrated by sluggish relief efforts.

Earlier on Monday, UN Chief Ban Ki-moon asked the Security Council to increase the number of military troops by 2,000, a nearly 30 percent increase, and the number of police officers by 1, 500, or 67 percent over current levels, for six months.

LeRoy said Haiti's neighbor, the Dominican Republic, has already pledged 800 troops to guard roads from its side of the island to Port-au-Prince - just one of two "humanitarian corridors" which will allow for speedier distribution of aid. The other thoroughfare will be established between Port-au-Prince and the country's northern seaports.

The additional 2,000 blue helmets will primarily be charged with escorting humanitarian operations, such as food distributions, said LeRoy, who noted that just from the World Food Program (WFP) 60,000 tons food are available at over 200 distribution points.

So far, the lack of a bolstered UN military presence has meant several humanitarian operations have been unescorted, increasing their risk to looting or violence.

Originally, the UN estimated that it needed roughly 1,250 additional troops and police. But LeRoy said that after speaking to staff members from the UN Mission, known as MINUSTAH, it became clear that more security was needed to accompany the hundreds of daily relief operations.

The request for additional troops and police comes amid criticisms that the United Nations has been slow in coordinating all the various aid efforts.

In the coming days, the UN Department of Peacekeeping Operations might ask the Security Council to expand MINUSTAH's mandate, said LeRoy and Susana Malcorra, who is in charge of UN field support operations.

Some countries have suggested that the UN's Mission does not have enough authority coordinating the international relief operations.

"Strengthening (the mandate) will make it more clear of what is the extent of coordination," said Malcorra. "We may need to push the boundaries of who uses what resources and where. It's not clear yet and we may come back to the Security Council."

Over the weekend, two WFP planes and a French cargo plane, carrying a field hospital, were reportedly turned away by the U.S. military, which took control of the nation's only airport -- with the consent of the Haitian government.

This prompted French Cooperation Minister Alain Joyandet to call for a UN investigation into the dominant U.S. role, going as far as calling it an "occupation."

U.S. Secretary of State Hillary Clinton shot back on Saturday saying the U.S. had no intention of taking power from Haitian officials.

"We are working to back them up, but not to supplant them," she said, according to local media reports.

LeRoy praised the American efforts and clarified that the U.S. is not operating under the United Nations umbrella.

"There is a clear division of labor," he said, adding that MINUSTAH is in charge of general security while the U.S. military offers security for American humanitarian operations.