* Oil supported by signs of U.S. economic growth
* Libyan protesters block oil pipeline
(New throughout, updates prices and market activity, new byline, changes dateleine, previously LONDON)
NEW YORK, March 28 (Reuters) - Brent crude oil rose for a fourth straight session on Friday, heading for its first weekly gain since February, on promising U.S. economic data and concern that possible Western sanctions on Russia's energy sector could disrupt global supplies.
The United States and NATO have voiced alarm over what they say are thousands of Russian troops massed near its western border with Ukraine. Russian President Vladimir Putin has reserved the right to send troops into Ukraine, home to a large population of Russian-speakers in the east.
U.S. crude oil rose for its third session on data showing consumer spending increased in February, lifted by an increase in services consumption, news that also buoyed the U.S. equities markets. However, a dip in consumer sentiment this month offered confirmation that economic growth slowed in the first quarter.
Brent rose 9 cents to $107.92 a barrel by 12:24 p.m. EDT (1623 GMT). U.S. crude gained 41 cents to $101.69, after settling up $1.02 in the previous session.
The U.S. benchmark was aided by a continued drawdown in oil stocks at Cushing, Oklahoma, the pricing point for the U.S. benchmark.
"I think that some of the same factors that have pushed us back above $100 are still driving the market, and there's still increased geopolitical risk from the situation in the Crimea as Russia continues to put troops along the border with Ukraine," said Gene McGillian, an analyst with Tradition Energy in Stamford, Connecticut.
U.S. crude rose over $2 over the past two sessions, and is up 2.3 percent on the week. Brent crude is up nearly 1 percent on the week, after 4 consecutive weeks of losses as it retreated from February's gains on the back of events unfolding in Ukraine.
U.S. crude's gains also outpaced Brent's for a third session, narrowing its discount to Brent <CL-LCO1=R> to $6.23 from as wide as $8.03 on Wednesday.
SUPPLY WORRIES UNDERPIN
Oil prices also continued to draw support from the Ukraine crisis, with the United States and the European Union agreeing to work together to prepare tougher economic sanctions in response to Russia's behaviour in Ukraine and to make Europe less dependent on Russian gas.
Russia is the world's top oil producer.
"Possible intensifying of sanctions led to higher perceived geopolitical risks by markets, hence supporting gains in benchmark crudes," Phillip Futures said in a note.
Other supply worries also underpinned prices.
In Libya, protesters have blocked a pipeline carrying around 30,000 barrels per day (bpd) of oil condensate from the southwestern al-Wafa oilfield to the Mellitah export port, state-owned National Oil Corp (NOC) said on Thursday.
NOC this week said Libya's output stood at 155,000 bpd, after the 130,000-bpd El Feel field, co-operated by Eni, had stopped producing. The 340,000-bpd El Sharara field shut weeks ago.
Libya's exports have been well below its capacity of around 1.25 million bpd since July 2013, when militias and protesters began blocking its major oil export terminals and oilfields.
(Additional reporting by Peg Mackey in London, Jacob Gronholt-Pedersen; Editing by William Hardy, Dale Hudson and David Gregorio)