A Security Council diplomat says Portugal's former prime minister Antonio Guterres topped the third informal poll of candidates seeking to succeed Ban Ki-moon as the next U.N. secretary-general, making him the clear front-runner for the job.

The diplomat, speaking on condition of anonymity because voting is supposed to be kept secret, said Slovakia's Foreign Minister Miroslav Lajcak, who finished next to last in the second "straw" poll, was the surprise second-place finisher.

The 15 Security Council members voted Monday afternoon on 10 candidates — five men and five women.

East European nations, including Russia, argue that they have never had a secretary-general and it is their turn. There has also never been a woman secretary-general and there is strong support to elect the first female U.N. chief.