The United Nations has taken charge of a multi-national protection force in eastern Chad following the end of the European Union's one-year mandate.  The full U.N. force is not yet in place, raising security concerns in an area already bracing for more refugees from Sudan's troubled Darfur region.

More than 2,000 troops remain from the 3,500 soldiers who made up the EU protection force.  They are the foundation of what is expected to be a more-than 5,000-member force under the command of the U.N. mission in Chad and the Central African Republic.

But because that force is not in place, the human rights group Amnesty International said civilians may now be at greater risk.

"This is going to result in a situation where there is a security vacuum," said Tawandra Hondora, deputy director of the Africa program at Amnesty International.  

With the U.N. force in neighboring Sudan at only 60 percent of its troop strength more than a year after taking over from African Union forces, Hondora said there is good reason to be concerned about the safety of refugees and internally displaced civilians.

"If it is going to take that long, we fear that civilians will be seriously exposed to greater harm in eastern Chad.  And the reason why we say this is because armed oppositions groups which are Chadian as well as armed opposition groups, which are Sudanese, have been known to attack civilians to recruit child soldiers from within the civilian population," Hondora said.

Amnesty International wants the U.N. Security Council to make sure the full deployment of troops is done in the shortest possible time.

With an alliance of Chadian opposition groups threatening to launch another attack on the capital Ndjamena at the end of the rainy season, the U.N. protection force is under pressure to become more actively involved in resolving Chad's long-running civil war beyond its current mandate to protect civilians and support relief efforts.

"You can keep people alive, but if you cannot stabilize the country, you are going to be providing that kind of support, that security for a really long time," said Erin Weir, who works for the advocacy group Refugees International.

Concern about a further decline in security in eastern Chad follows this month's International Criminal Court arrest warrant charging Sudanese President Omar Hassan al-Bashir with crimes against humanity in Darfur.

Khartoum responded by expelling 13 international aid agencies last week.  Hondora said that could bring more Sudanese refugees across the border into Chad.

"If that situation is not resolved quickly, we may see population flows from Sudan, Darfur into eastern Chad increasing the population and also increasing the security risks," said Hondora.

The new U.N. protection force recognizes that danger, saying it is preparing for the possible influx of more Sudanese refugees as aid levels decline with the expulsion of non-governmental organizations.