Vienna, March 14 : External electricity supplies have been restored at Ukraine's now-defunct Chernobyl nuclear power plant, four days after its disconnection from the power grid, the Vienna-based International Atomic Energy Agency (IAEA) said. Ukraine's regulatory authorities told the IAEA that Ukrainian specialist teams repaired one of the two damaged power lines at Chernobyl on Sunday, enabling all required off-site power to be delivered to the plant, Xinhua news agency quoted the UN nuclear watchdog as saying in a statement. The plant will be connected to the Ukrainian electricity grid on Monday morning, according to Ukraine's regulator. The Chernobyl plant was disconnected from the power grid on March 10 and has been operating on backup diesel generators. The plant is currently controlled by Russian armed forces. "This is a positive development as the Chernobyl nuclear power plant has had to rely on emergency diesel generators for several days now," the IAEA Director-General Rafael Grossi said. "However, I remain gravely concerned about safety and security at Chernobyl and Ukraine's other nuclear facilities." The Chernobyl nuclear plant, some 110 kms north of Kiev, witnessed the worst nuclear accidents in human history on April 26, 1986. /IANS