* 2.2 mln people displaced since civil war started in Dec 2013

* South Sudan oil output has shrunk due to fighting

JUBA Nov 18 (Reuters) - South Sudan President Salva Kiir said on Wednesday his country will struggle to resettle thousands of refugees and those displaced internally during nearly two years of war, saying low world oil prices which had depleted government coffers.

South Sudan has been mired in conflict since December 2013, when clashes broke out in the capital Juba between troops loyal to Kiir and soldiers backing Riek Machar, the former vice president.

Facing heavy international pressure and the threat of sanctions, Kiir and Machar signed a peace deal in August, but the civil war, fought mostly in oil-producing areas, has displaced more than 2.2 million people, including about 600,000 who sought refuge in neighbouring countries.

Production, which stood at 245,000 barrels per day before violence erupted, is down by roughly a third.

Kiir said a slide in oil prices on international markets has eaten into government reserves and he called on donors to help South Sudan with its humanitarian needs.

"I have signed the peace agreement, but the implementation of this peace comes with challenges and high cost," Kiir said in speech in Juba. "We have the challenges of repatriation and rehabilitation of internally displaced persons and returnees."

"We need support from our development partners and friends in order to achieve a smooth implementation of the peace agreement", Kiir added.

Kiir on Wednesday once again accused Machar's troops of violating the ceasefire. "As I speak, the rebels are still planning for more attacks on Malakal, Tharjath, Bentiu, Rubkuna, Guit, Leer and Pan Akuach," he said.

A day earlier the rebels said Kiir's forces had attacked a military base in Unity State, an oil producing region. (Reporting by Denis Dumo; editing by Drazen Jorgic and Richard Balmforth)