WASHINGTON (AP) — Secretary of State John Kerry says he will travel to London to meet Russian Foreign Minister Sergey Lavrov (SEHR'-gay LAHV'-rahf) on Friday in a last-ditch bid to avert a new crisis over Ukraine.

Kerry told Congress on Wednesday he will make the trip to try to calm rising East-West tensions ahead of a weekend referendum in Ukraine's Crimea region on whether to join Russia. Sunday's vote in the largely pro-Moscow peninsula is widely expected to endorse its secession from Ukraine. Western powers say they won't recognize the referendum because it violates Ukraine's constitution. Russia maintains it is a legitimate expression of the Crimean people's desire for self-determination.

Kerry has been unsuccessfully trying for more than a week to broker a meeting between Russian and Ukrainian and European diplomats to ease the situation.