AFP - Two months after Haiti's January 12 earthquake, aids groups were still scrambling Friday to provide for the 1.3 million people left homeless amid growing insecurity in Port-au-Prince.

The kidnapping of two female aid workers, a Belgian and a Czech, cast a shadow over the relief operations carried out by more than 300 foreign organizations in Haiti.

It was the first abduction to occur in Haiti since the earthquake, Haitian police said.

The two were freed Thursday, after spending six days in captivity, according to their employer, Medecins Sans Frontieres (MSF; Doctors Without Borders).

The head of the Haitian police anti-kidnapping unit dealing with the investigation, Francois Dossous, told AFP he was "a little worried" about the case, suggesting it might herald a crime wave against the thousands of foreigners in Haiti.

"I've told my superiors about my concerns," he said.

Dossous said the abductors were Haitians, but there were clues to suggest they were criminals who had been deported back to Haiti after being convicted abroad, perhaps from Canada or the United States.

Dossous also confirmed the victims' nationalities, and said they had not been sexually assaulted during their sequestration.

He concluded that a ransom had been paid.

MSF refused to give any details of the kidnapping or what resulted in the women's freedom, other than to say it was "immensely relieved" they had been let go.

Some of the thousands of aid workers in Haiti said the kidnapping made them more alert. A few said their groups were now taking extra precautions, but refused to detail them.

An Australian security officer for one aid group, speaking on condition of anonymity, warned that "you could soon see a rise in the number of kidnappings -- that's the information we're getting."

Simon Collins, an Irish doctor with MSF working in a camp of thousands of homeless Haitians, said his group had always sought to work among the people it helped, despite security risks.

"It's the idea of being here, seeing what's going on, on the ground, at the frontline, not being distant in an air-conditioned office, but actually being on the ground and among the people," he said.

Aid groups said they still faced huge challenges in Haiti.

Most notably, nearly half of Haiti's homeless still need emergency shelter before the onset of Haiti's extremely heavy rainy season in the next few weeks.

The UN Office for the Coordination of Humanitarian Aid said it hoped to have all 1.3 million under cover of tents or tarpaulins by the end of April.

The Red Cross has provided 99,000 temporary shelter kits for families and meals for more than one million people since starting post-quake operations, according to the American Red Cross Friday.

The US military, though, was cutting its deployment to Haiti from 11,000 personnel to 8,000 after determining that the security and medical situation on the ground no longer required so many troops.

A US official, declining to be identified so he could speak more freely, said the international aid effort had so far gone "reasonably well," considering the initial problems faced, such as getting supplies in through a damaged airport and a destroyed seaport that had be rebuilt.

"You have to realize that we flew in much more aid than in the (1948-1949) Berlin airlift," with planes landing every 30 seconds at the peak of the inflow, he said.

"Obviously the UN has been criticized -- some of that is warranted, some of it unwarranted," he said.

But, he added: "Not enough credit has been given on what went right in Haiti. That said, the job is not finished. The rains are coming. And there is still huge work ahead."