Oil prices have briefly fallen below $30 a barrel on international markets for the first time since April 2004, before recovering again.

Brent crude, used as an international benchmark, fell as low as $29.96, but bounced back to trade at $30.22. Oil prices have fallen by 70% in the past 15 months.

Earlier, Russia's Prime Minister, Dmitry Medvedev, warned tumbling oil prices could force his country to revise its 2016 budget.

He said that the country must be prepared for a "worst-case" economic scenario if the price continued to fall.

Taxes from oil and gas generates about half the Russian government's revenue, BBC says.

The 2016 federal budget that was approved in October was based on an oil price of $50 a barrel in 2016 - a figure President Vladimir Putin has since described as "unrealistic".

Government departments have been ordered to cut spending by 10%, repeating a policy imposed in 2015, Reuters reported.

Pensions and pay for government workers will be protected from the cuts, which could save as much as 700bn roubles $9.1bn).

Finance minister Anton Siluanov said that the Russian budget could only be balanced at an oil price of $82 a barrel.