Yemeni security officials said clashes were underway hours before a scheduled cease-fire between Shi'ite Houthi rebels and forces allied with the internationally recognized government.
The officials say Sunday's clashes took place in several areas, including the provinces of Jawf, Sana'a, and Taiz, where the Houthis have gained ground despite Saudi-led airstrikes.
The officials, who are neutral in a conflict that has split the armed forces, spoke anonymously because they were not authorized to brief reporters.
The cease-fire is scheduled to begin at 11:59 p.m. (2059 GMT) Sunday.
The Saudi-led coalition's spokesman said Friday it is ready to commit to a cease-fire as long as the rebels abide by a U.N. Security Council resolution that calls for them to withdraw from cities, including the capital, Sana'a, and hand over their weapons.