A US Air Force F-16 fighter jet takes part in the US-led Saber Strike exercise flies in Estonia's airspace, June 6, 2018. (Reuters)

Various countries have begun training Ukrainian pilots on F-16 warplanes as Kiev seeks to secure the US-made jets to supplement its forces for its counteroffensive against Russia.

A number of countries, including Poland, have begun training Ukrainian pilots in flying F-16 fighter jets, EU foreign policy chief Josep Borrell said on Tuesday.

The EU Foreign Policy Chief Josep Borrell announced, "I am happy that finally the training of the pilots of the F16s has started in several countries, it will take time but the sooner the better."

Borrell, who spoke to reporters ahead of a Foreign Affairs Council meeting, said Poland is taking part in the process.

Ukraine has taken the choice of training its pilots on the use of F-16 jets without having secured any yet.

Yuriy Sak, an advisor to the Ukrainian Defense Ministry, said the Netherlands is expected to be the first country to send F-16s to Kiev.

"The Netherlands are in a position to be [the] first [country delivering fighters]," as reported by Politico.

Earlier on Monday, Dutch Foreign Minister Wopke Hoekstra said Western backers of Ukraine should make a collective decision in regards to supplying Ukraine with the jets instead of individual contributions, adding that the issue must be negotiated within a larger coalition.

Sak previously revealed that Kiev is looking to be supplied with 50 jets in the form of contributions made by its allies.

The official said to The Washington Post on Saturday that the first batch of fighter jets is expected to arrive in Ukraine in late September or early October.

Last week, US President Joe Biden told G7 leaders that Washington will endorse supplying advanced warplanes including F-16s to Ukraine and will support efforts to train Kiev's pilots.

After the US' approval to supply Ukraine with a number of F-16 Fighting Falcon, Zelensky immediately praised it as a "historic decision", saying that it would "greatly enhance our army in the sky."

It is worth noting that the Ukrainian President has been desperate for fighter jets, repeatedly pushing for advanced Western jets, but Kiev's international supporters had balked at doing so until recently.

"We have freedom, give us wings to protect it," Ukrainian President Volodymyr Zelensky told UK Members of Parliament as he toured European countries in the hope of securing fighter jets back in February.