HAVANA, Cuba — A unilateral ceasefire declared by the Marxist FARC rebels at the start of peace talks with the Colombian government ended on Sunday after the government refused to join the truce, the group said.

"With pain in my heart, we have to admit that we return to the stage of war that nobody in this country (Colombia) wants," FARC lead negotiator Ivan Marquez told reporters before going into the latest session of the talks aimed at ending Colombia's long, bloody conflict.

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The FARC, or Revolutionary Armed Forces of Colombia, declared the ceasefire when the talks began on November 19 in Havana, and gave the government two months to also lay down its arms.

Colombian President Juan Manuel Santos rejected the ceasefire from the beginning, saying the government would maintain the military pressure to keep FARC at the negotiating table.

Colombian officials have called the ceasefire a sham to gain international favor and accused the rebels of continuing their attacks.

Government forces have continued to attack and kill the rebels in their remote strongholds in the jungles and mountains of Colombia. They say the rebels may be planning a new offensive.

Marquez did not disclose their plans, but urged Santos to reconsider the decision not to lay down arms.

The two sides have been fighting since the formation of the FARC as a communist agrarian movement in 1964 in what is now Latin America's longest-running insurgency and a relic of the Cold War.

Tens of thousands of people have been killed and millions displaced in the conflict, which the FARC says is aimed at ending Colombia's long history of social inequality and the concentration of land and wealth in relatively few hands.

Officials say the FARC has been weakened by a U.S.-backed, 10-year-long government offensive.

But the group still has an estimated 9,000 fighters capable of continuing to inflict damage on Colombia's infrastructure and slow the government's plans to increase foreign investment in mining and oil operations.

The agenda for the talks calls for the two sides to address a number of difficult issues, starting with rural development.

In recent days, they have publicly disagreed about a sweeping land redistribution proposal by the FARC to hand over 25 million hectares (62 million acres), or more than 20 percent of the country's land, to the poor.

Government lead negotiator Humberto de la Calle this week called for a quicker pace to the talks, which Santos has said he wants ended by November. 

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