Five of India’s 40 AN-32 military transport aircrafts being upgraded in Ukraine have gone missing "without a trace"; Ukrainian diplomat says the government is unable to help.

India says five of its 40 AN-32 military transport aircrafts have gone missing "without a trace" while the planes underwent upgrades in Ukraine.

"These five aircraft are almost lost as it is difficult to trace them and diplomatic efforts to find their whereabouts have failed," the website DefenseNews quotes an Indian Air Force official as saying.

In 2009, India signed a contract with Ukraine's state-owned arms trading agency, Ukrspetsexport Corp., to upgrade its 104 AN-32 transport aircrafts at a cost of US $400 million, as the fleet had reached its life expectancy.

The upgrade program started in 2011 and was set to run through 2017.

Under the deal, the modernization of 40 warplanes should have been completed in Ukraine at Kiev-based Antonov State Co. facilities, while the 64 others were set to be upgraded in India at the Air Force's Kanpur-based base, under a technology transfer from Ukraine.

The upgrade was expected to extend the life expectancy of the transporters from 25 to 40 years and provide them with improved avionics, a modernized cockpit and an increase in capacity from 6.7 to 7.5 tons.

However out of 40 warplanes sent to Kiev, only 35 made their way back home.

The remaining five have been "lost without trace".

The local upgrade of the remaining 64 AN-32s has been halted as Ukrainian engineers departed and supplies of spare parts stopped, according to the Indian Air Force.

A diplomat from the Ukraine Embassy said Antonov must resolve this issue with the Indian Air Force, and that the government cannot help.

Antonov officials were unavailable for comment.