GENEVA, Sept 15 (Reuters) - The U.N. refugee agency said on Tuesday that over 100,000 people have been internally displaced by the renewed Yemen conflict and thousands more have fled by sea to Djibouti.

"Humanitarian access remains a major challenge. Insecurity, damaged roads, telecommunications disruptions and movement restrictions are affecting operations," UNHCR said in a statement.

Yemen's Iran-aligned Houthis have stepped up attacks on Saudi cities and energy infrastructure while advancing along Yemen's Red Sea coast towards the Bab el-Mandeb Strait, a key shipping route. Responding to the Houthi offensive, the Saudi and Yemeni air forces have bombarded Houthi targets.

(Reporting by Emma Farge, Editing by Friederike Heine)

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