Iran ? Iranian and Russian engineers began loading fuel into Iran’s first nuclear power plant today, a major milestone as Tehran forges ahead with its atomic program despite U.N. sanctions.

The weeklong operation to load uranium fuel into the reactor at the Bushehr power plant in southern Iran is the first step in starting up a facility the U.S. once hoped to prevent because of fears over Tehran’s nuclear ambitions.

Russia, which helped finish building the plant, has pledged to safeguard the site and prevent spent nuclear fuel from being shifted to a possible weapons program. After years of delaying its completion, Moscow says it believes the Bushehr project is essential for persuading Iran to cooperate with international efforts to ensure Iran does not develop the bomb.