The director-general of the agency, Rafael Mariano Grossi, said Sunday Ukrainian staff members are now required to seek approval for any operation, even maintenance, from the Russians, and that they have impeded normal communications by switching off some mobile networks and internet at the site.

Ukraine's regulatory authority said that phone lines, as well as e-mails and fax, are no longer working. Grossi said he is ``extremely concerned about these developments,'' adding that for the plant to operate safely, ``staff must be allowed to carry out their vital duties in stable conditions, without undue external interference or pressure.''