Russian oil giant Lukoil on Thursday called for an immediate halt to fighting in Ukraine, one of the first major domestic firms to speak out against Moscow's invasion of its pro-Western neighbor.

The board "expresses its concern over the ongoing tragic events in Ukraine and its deepest sympathy to all those affected by this tragedy," the company said in a statement. 

"We stand for the immediate cessation of the armed conflict and fully support its resolution through the negotiation process and through diplomatic means," its note added.

Russian President Vladimir Putin has pressed ahead with his assault against Ukraine, which he announced last week despite warning from the West of sanctions that would cripple the economy.

The penalties, now introduced, have seen the ruble plunge and the Moscow stock exchange closed for several days, with the country on the brink of its worst economic crisis for decades.

Prominent Russian businessmen outside of the country have been expressing concern over the economic impact of the invasion, but Lukoil's statement is among the first such statements from a major company at home.

Lukoil said it would continue in its efforts to "provide reliable energy supplies to consumers around the world" and that it was "committed to strengthening peace, international relations and humanitarian ties."

As part of the sanctions package, the French government on Thursday said it had seized a superyacht owned by a company linked to Igor Sechin, chief executive of Russian energy giant Rosneft and close Putin.