Russia's defence ministry said on Thursday Ukrainian forces tried to seize the Russian-controlled Zaporizhzhia nuclear plant in southern Ukraine and "measures had been taken" to destroy the opposing troops, including use of military aviation.
In a statement, the ministry said that up to 60 Ukrainian troops had crossed the Dnipro river, which divides territory held by the two sides, in boats at 6 a.m. local time (0300 GMT). It called the operation a "provocation" aimed at disrupting a planned visit by International Atomic Energy Agency inspectors to the nuclear plant.
It also accused Ukraine of shelling both the meeting point of the IAEA delegation, and the Russian-held Zaporizhzhia plant itself.
Ukraine said it was Russian forces that were shelling the plant, with its president's chief of staff accusing Moscow of trying to "wreck" the IAEA mission. The plant's operator said one of the reactors has been shut down as a result.
A Reuters reporter in Russian-controlled Enerhodar witnessed increased military activity on Thursday, with Russian soldiers running about and helicopters flying overhead and firing at targets on the ground. The reporter said a residential building was struck by shelling, forcing people to take cover in a basement.
Separately, Russian state-owned news agency RIA cited local Russian-installed official Vladimir Rogov as saying that the Ukrainian troops had landed between one to two kilometres (0.62-1.24 miles) away from the nuclear plant.
Reuters could not immediately verify the reports.
The mission by the United Nations' nuclear watchdog aims to assess risks from the ongoing hostilities in the area.
The plant was captured by Russian forces in March, but has been operated by Ukrainian staff. It remains near the front lines, and has come under repeated shelling in recent weeks, raising fears of a nuclear disaster. Both Ukraine and Russia have repeatedly accused each other of shelling the facility.
(Reporting by Reuters; Editing by Tomasz Janowski)