Ukraine's new President Volodymyr Zelenskiy on Wednesday appointed former economy minister Aivaras Abromavicius to the supervisory board of the state defence conglomerate Ukroboronprom, a decree published on his website said.

Zelenskiy has also appointed Oleksandr Danylyuk as secretary of the national defence and security council. A top reformist, Danylyuk was finance minister under Poroshenko but fell out with Prime Minister Volodymyr Groysman.

The appointments come amid reports of a continued Russian troop building up in Crimea. Defense One reported Wednesday that "five S-400 anti-aircraft missile batteries, plus additional troops and fighters" have been deployed to Crimea in the last eighteen months.

The report, which cites U.S. officials and satellite images, adds that the "significant" build up allows "Moscow better defend the Black Sea and threaten Europe and the Middle East."

Zelenskiy, a former comedian, was elected despite having no prior political experience, so investors are watching closely to see how many reform-minded people he brings into cabinet

Lithuanian-born Abromavicius was brought in as a reformer under previous president Petro Poroshenko to run the Economy Ministry, but quit in February 2016 in frustration at what he said were attempts by vested interests to block his reforms.

Ukroboronprom was under scrutiny during the election campaign because of a corruption investigation by local journalists into the son of a close Poroshenko ally.

The investigation alleged Ukroboronprom's involvement in a scam to smuggle used Russian military parts into Ukraine and sell them to the army at inflated prices. Ukroboronprom denied wrongdoing and called the reporting "manipulative".