* Washington includes 20 prominent Russian business men to sanctions list
* Gunvor-founder Timchenko included in list; US says close Putin ally
* Crude weighed by stronger U.S. dollar, seasonal slump in demand
By Jacob Gronholt-Pedersen
SINGAPORE, March 21 Brent crude fell towards $106 per barrel on Friday, on track for a fourth weekly loss weighed down by a stronger dollar and seasonal slump in demand, while fresh U.S. sanctions against Russia could inject a new risk premium into the market.
Brent rose on Thursday after Washington expanded sanctions to 20 more prominent Russians, including allies of Russian President Vladimir Putin, in the latest sign of mounting tensions over Moscow's annexation of Crimea.
On Friday, Brent was down 20 cents at $106.25 per barrel by 0320 GMT, after settling 60 cents higher.
U.S. crude was 38 cents lower at $98.52 per barrel. Crude for May delivery, which became the front-month contract on Friday, had settled 27 cents lower. The U.S. contract was headed for its third weekly loss.
"Brent has approached the lower band of its $105-$110 trading range, which yesterday incentivised investors to come into the market. So we are seeing a bit of profit taking this morning," said Chee Tat Tan.
"Also, the dollar has regained some momentum and this strengthening has hurt some external demand for crude oil," said Tan.
The greenback was underpinned near a three-week high by a spike in U.S. bond yields. Against a basket of major currencies, the U.S. dollar was trading at 80.161, not far from the high of 80.354, a level not seen since late February.
A strong dollar makes commodities priced in the currency expensive for holders of other currencies.
While the West has failed to impose broad trade sanctions against Russia over its annexation of Ukraine's Crimea region, the United States on Thursday moved to expand a sanctions list to include Russian billionaire Gennady Timchenko, co-founder of Swiss trading firm Gunvor and considered by Washington to be a close ally of President Vladimir Putin.
Gunvor, which had a turnover of $93 billion in 2012, grew rapidly by trading large volumes of oil from Russian state companies such as Rosneft at the end of last decade, but has since then ceded its leading positions and now focuses on trading in Europe and Asia.
"Timchenko activities in the energy sector have been directly linked to Putin. Putin has investments in Gunvor and may have access to Gunvor funds," the U.S. Treasury said in a statement.
The move forced Timchenko to sell his near 50 percent stake in the trading empire.
President Barack Obama threatened broad penalties against key sectors of Russia's economy if Moscow moves deeper into Ukraine. Senior administration officials said many parts of the Russian economy could be targeted, including energy, defence, mining and financial services sectors.
Meanwhile, European leaders will agree to expand a list of those subject to travel bans and asset freezes on Thursday but stop short of harder-hitting measures against Russia, biding their time to retain EU unity and gauge Moscow's reaction. (Reporting By Jacob Gronholt-Pedersen; Editing by Michael Perry)