(CNN) -- Al Qaeda in the Arabian Peninsula is threatening to kill the 73 Yemeni troops it is holding hostage if the government does not release al Qaeda prisoners.
In a statement issued late Thursday, the group advised family members of the hostages to push the government to cooperate, but a senior security official in the southern province of Abyan, where the troops are being held, said the government would not give in to the group's demands.
"We will work on freeing the soldiers being held by the militants, but only by reasonable means. The government will not set free any militants. This will only make the terror crisis even worse," said the security official, who is not authorized to talk to media.
The official said three of the troops had already been killed.
The threat of more killings came as Yemen mourned the approximately 200 troops killed this week by al Qaeda in three Yemeni provinces.
President Abdurabu Hadi vowed Thursday to step up government efforts to fight al Qaeda, saying he will not allow Yemen to fall into the hands of extremists.
A delegation from the Yemen Military Committee, the highest security authority in the country, reached Abyan on Wednesday as part of an investigation into how al Qaeda in the Arabian Peninsula (AQAP) has been able to score consistent victories in the region over the past week.
Western officials describe AQAP as al Qaeda's most dangerous affiliate.
"We expected obstacles, but the president will do all in his power to uproot the terror militants from the country," said Yahya al-Arassi, the president's spokesman. "This is a promise he gave the people."
AQAP has tried to win support by portraying itself as a defender of Yemenis against a U.S.-backed dictatorship. The group is linked to jihadist fighters who have taken control of swathes of southern Yemen.
The United Nations refugee agency said Friday that tens of thousands of civilians are fleeing tribal clashes in the north and fighting between government troops and militants in the south.
In the Haradh governorate, north of the capital, Sanaa, tribal clashes over the past three months have displaced about 52,000 people, Yemeni authorities have said, according to the spokesman for the U.N. High Commissioner for Refugees, Adrian Edwards.
Another 314,000 Yemenis were already displaced in the country's north, he said in a news release.
A peace agreement was signed in June 2010 between the government and Al-Houti forces but the situation in northern Yemen is volatile and insecure, the UNHCR said.
"We continue to run two camps for displaced Yemenis in the north and have been providing assistance to internally displaced persons in the camps and in host communities," Edwards said.
In the south, at least 1,800 people have been displaced by recent fighting between government troops and militants in the Abyan governorate, the UNHCR said. They have joined more than 150,000 others in the south who have been displaced since last May, when the conflict began.