Egypt's prestigious Islamic institute al-Azhar urged the Nigerian Muslim group Boko Haram group Tuesday to free more than 200 schoolgirls it kidnapped and has threatened to sell into slavery.

Al-Azhar, which runs the main Sunni Islamic university in the region, said harming the girls "completely contradicts the teachings of Islam and its tolerant principles."

U.S. actress Angelina Jolie on Tuesday condemned as "unthinkable cruelty and evil" the kidnapping of over 200 schoolgirls in Nigeria by Boko Haram Islamists.

The star was speaking in Paris about the themes of her latest film "Maleficent" for Disney, in which she plays a vindictive fairy driven to curse an infant princess.

Egypt's prestigious Islamic institute Al-Azhar urged the Nigerian Muslim group Boko Haram group Tuesday to free more than 200 schoolgirls it kidnapped and has threatened to sell into slavery.

Al-Azhar, which runs the main Sunni Islamic university in the region, said harming the girls "completely contradicts the teachings of Islam and its tolerant principles."

Nigerian parents on Tuesday said their worst fears about their daughters' fates had been confirmed after Boko Haram, which kidnapped more than 200 schoolgirls last month, threatened to sell the hostages as "slaves."

Abubakar Shekau, who leads the Islamist group which has killed thousands in a five-year uprising, claimed responsibility for the shocking mass abduction on April 14 in the Chibok area of northeastern Borno state.

Niger Delta gunmen have released two Nigerians they kidnapped two days ago, but kept three Dutch nationals who were abducted at the same time, one of those freed tweeted on Tuesday.

Environmental activist Sunny Ofehe tweeted that he and another kidnap victim were "released in the creek of Niger Delta last night by gunmen! The other 3 colleagues are yet to be freed."

The United States said Monday that it is concerned that many of the 276 Nigerian schoolgirls kidnapped in northern Nigeria three weeks ago have been moved out of the country.

State Department spokeswoman Marie Harf shared Washington's assessment after local officials in northeastern Nigerian told Agence France Presse the girls had likely been taken to nearby Chad or Cameroon.

Scores of Boko Haram gunmen riding in armored vehicles razed a remote northeast Nigeria town on Monday and opened fire on residents who tried to flee into neighboring Cameroon, witnesses said. 

The targeted town of Gomboru Ngala falls in Borno state, home base of the Islamist group which on Monday claimed the shocking kidnap of more than 200 schoolgirls in Chibok, also in Borno.  

Boko Haram on Monday claimed responsibility for the abduction of hundreds of schoolgirls in northern Nigeria that has triggered international outrage, threatening to sell them as "slaves".

"I abducted your girls," the Islamist group's leader Abubakar Shekau said in the 57-minute video obtained by Agence France Presse, referring to the 276 students kidnapped three weeks ago from their boarding school in Chibok, Borno state.

A police officer and a detainee were shot dead overnight in an attack in northern Cameroon blamed on Nigerian Islamist extremist group Boko Haram, a security source said Monday.

"Boko Haram attacked the unit in the night. (The attackers) were looking for a detained member. They left with him and with other people who were in the same cell" of the paramilitary police in Kousseri, said the source, who asked not to be named.

Nigerian President Goodluck Jonathan on Sunday vowed to ensure the release of 223 schoolgirls abducted by suspected Islamists, saying he has sought help from U.S. President Barack Obama to overcome the nation's security challenges.

"We promise that anywhere the girls are, we will surely get them out," Jonathan said in a live broadcast on radio and television.