DAKAR, Jan 18 (Reuters) - Senegal's forces are at the Gambian border and will enter at midnight if veteran Gambian President Yahya Jammeh refuses to leave power, Colonel Abdou Ndiaye, a spokesman for the Senegal army, told Reuters.

Jammeh, who lost a Dec. 1 election to coalition leader Adama Barrow, said he will not step down due to irregularities in the vote. His official mandate ends at midnight.

"We are ready and are awaiting the deadline at midnight. If no political solution is found, we will step in," Ndiaye said.

(Reporting by Diadie Ba; Writing by Edward McAllister; Editing by Matthew Mpoke Bigg and Robin Pomeroy)

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