A 6.1-magnitude aftershock hit Haiti's already devastated capital early Wednesday as international search and rescue teams continued their work in the quake-shaken country.

The aftershock, the most powerful since the Jan. 12 earthquake, hit Port-au-Prince at 6:03 a.m. local time (1103 GMT). Its epicenter was about 60 km west of the capital, according to the U.S. Geological Survey. There is no report of casualties or damage yet.

One week after the 7.3-magnitude earthquake that hit the poorest country in the Western Hemisphere, a massive international aid effort is underway as 43 search and rescue teams continue their work.

So far, 90 people had been pulled alive from the rubble, U.N. Secretary-General Ban Ki-moon said Tuesday, noting "rapid progress" despite logistical difficulties.

Paralysed transport, mountainous geography, and the collapse of infrastructure and telecommunications have prevented aid from quickly reaching the victims.

Blockages on key roads still hamper the distribution of humanitarian aid and the Caribbean nation's only airport, in Port-au-Prince, is working at full capacity, with 100 flights landing a day.

"We're doing our best to get as many flights in as possible," said U.S. Deputy Ambassador to the U.N. Alejandro Wolff.

Only 18 aircraft can be parked in the area at a time and U.S. troops, which now run the facility, ordered it closed at one point last week because there was no more room.

Delivering food has proved extraordinarily tricky. Out of a total of roughly 3 million affected Haitians, the World Food Program was feeding 200,000 people, a figure expected to climb to 1 million by the end of the week, Ban said.

The U.N. chief acknowledged the sluggish pace at which aid was getting into the hands of the most needy and urged for patience, saying that "the situation is overwhelming."

Moreover, aid work has suffered from a lack of leadership due to personnel losses among national and international authorities and a lack of coordination among different aid groups.

The U.N. peacekeeping mission in Haiti was hard hit by the quake, with some 46 staffers confirmed dead and more than 500 still unaccounted for.

Haiti's Civil Defence Department estimated on Tuesday that the quake had killed 75,000 people, injured 250,000 and left one million homeless.

With millions starving and in need of shelter, tensions have risen, with reports of looting and violence. But U.N. peacekeeping chief Alain LeRoy downplayed the violence, calling the number of incidents "isolated."

"Of course, violence is still increasing," he said. "There are terrible cases but it's not widespread."

The U.N. is working with the Haitian government to get the security situation under control. Some 4,000 Haitian police and 3,500 peacekeeping troops patrol the streets and distribute humanitarian aid in Port-au-Prince.

Edmond Mullet, Ban's acting special representative, said 200 more peacekeeping troops outside Port-au-Prince had also been brought in.

Meanwhile, the U.N. Security Council on Tuesday approved Ban's suggestion of sending 3,500 extra troops and police officers to beef up security in Haiti.

"I am grateful to the Security Council for its swift action today," Ban told reporters, adding that in sending more security, the Council was sending a clear message of solidarity with the Haitian people.

The next critical step was deploying the soldiers and police officers as quickly as possible, which depended on the pledges made by individual countries, Ban said.

(Xinhua News Agency, January 21, 2010)