Hungarian Prime Minister Viktor Orbán has ordered a halt to the transit of natural gas through his country into Ukraine from July, according to a decree published overnight.

The decree follows Orbán's stated aim of pressuring the neighbouring country to restore the flow of oil through the Druzhba pipeline, which was damaged in a Russian strike.

"As long as Ukraine does not give us oil, it will not get gas from Hungary," Orbán said on Wednesday on his Facebook page.

According to experts, the blocking of gas transit into Ukraine raises serious legal questions.

The gas trade is in the hands of private companies, including firms that trade in the energy commodity and those that handle its transport through pipelines. In Hungary, this is pipeline operator FGSZ, a subsidiary of oil and gas group MOL.

Traders purchase transit capacities from pipeline operators, which are allocated at auction.

Orbán's decree prohibits Hungarian operator FGSZ from offering capacities for transit to the entry points into Ukraine from July onwards.

The company has already sold capacities for the second quarter, until June. Any interference with those contracts would have exposed the government to enormous compensation claims.

Ukraine received around 44% of its gas imports via Hungary last year, according to the state gas grid operator. Poland and Slovakia are also important transit countries for Ukrainian gas imports.

The Hungarian prime minister, seen as Russia's most important ally in Europe, faces a parliamentary election on April 12 and is accused of using its leverage over Ukraine to win votes.