UNITED NATIONS (AP) -- The UN investigator for human rights in North Korea said Wednesday he’s concerned about the growing number of asylum seekers leaving the country, with nearly 870 arriving in Thailand in the first quarter of this year.

Marzuki Darusman, the United Nations rights rapporteur for the country, told the General Assembly that many North Korean asylum seekers are exploited by traffickers, with women and children especially vulnerable.

``It is difficult to estimate the number of people leaving (North Korea) at any given stage, given that it takes months, and sometimes years,“ before they reach a country where proper asylum statistics are kept, Darusman said.

But he said nearly 870 asylum seekers from North Korea had arrived in Thailand between January and April 2011 after traveling through other countries.

Darusman, the former Indonesian attorney-general, said there were only 40 North Korean asylum seekers reported in Thailand during all of 2004. He said the number had grown steadily since then, peaking at 2,482 last year.

The U.N. investigator also underscored North Korea’s critical food situation, and said a harsh winter and a squeeze on commercial imports had further raised worries about food security.

``Reports indicate that current rations provided by (the North Korean government) can meet well less than half of the daily calorific needs for 68 percent of the 16 million population receiving public food rations,” he said. ``Most people struggled to make up this deficit through alternative means as they do not have the necessary purchasing power.”

He said he was especially concerned about children, pregnant and lactating women, the elderly, large families and people with disabilities.

As for North Korea’s own rights record, Darusman also said that freedom of speech and expression remain extremely limited in the secretive communist-run country. He added that criticism of the government and its leaders are strictly curtailed, punishable by arrest and incarceration.