Slovak natural gas pipeline operator Eustream said on Tuesday it would offer additional capacity in its new link allowing shipments from the European Union to Ukraine, raising possible deliveries by about 17 percent.

Eustream said it was launching an "open season" bidding process for capacity of 4.5 million cubic metres per day, in addition to about 27 mcm -- which amounts to about 10 bcm per year -- available since the pipeline was opened in September.

"Eustream provides additional pipeline capacity of 4.5 million cubic meters per day (46,800 MWh) in response to technical measures taken at the Ukrainian side," the company said in a statement.

Bidding will run until Nov. 19, and the capacity will be available from the beginning of the next year until the end of 2019. Up until January 2015, the extra capacity will be made available to all parties on a first-come, first-served basis.

The new connection, using an upgraded unused old pipeline running a short stretch over the two countries' common border, was put into operation after Russia halted gas shipments to Ukraine in June in a row over unpaid bills.

Relations between Moscow and Kiev have been at an all-time low since Russia's annexation of Crimea and support for separatists in eastern Ukraine.

Ukraine has maintained the transit of Russian gas for EU countries.

The Slovak connection can supply more than a fifth of Ukraine's gas needs. Ukraine also gets small amounts of gas from Poland and covers part of its needs from domestic production.

Ukraine, Russia and the EU signed a deal last Thursday that will see Moscow resume supplies to its former Soviet neighbour over the winter months in return for payments funded in part by Kiev's Western creditors.