* Both benchmarks mark about 30 pct gain in Q1
* U.S. warns over oil trading with Iran, Venezuela
* Barclays sees higher oil prices in Q2 on supply constraints
* U.S. drillers cut most oil rigs in a quarter in three years (New throughout, updates prices, market activity and comments to settlement)
By Stephanie Kelly
NEW YORK, March 29 (Reuters) - Oil prices rose about 1 percent on Friday, posting their biggest quarterly rise in a decade, as U.S. sanctions against Iran and Venezuela as well as OPEC-led supply cuts overshadowed concerns over a slowing global economy.
The May Brent crude oil futures contract, which expired Friday, gained 57 cents, or 0.84 percent, to settle at $68.39 a barrel, marking a first-quarter gain of 27 percent. The more-active June contract settled up 48 cents at $67.58 a barrel.
U.S. West Texas Intermediate (WTI) futures rose 84 cents, or 1.42 percent, to $60.14 a barrel, and posted a rise of 32 percent in the January-March period.
For the two benchmarks, the quarterly rise was the biggest since the second quarter of 2009, when both gained about 40 percent.
U.S. sanctions on Iran and Venezuela have boosted prices this year. Washington is keen to see that Malaysia, Singapore and others are fully aware of illicit Iranian oil shipments and the tactics Iran uses to evade sanctions, a U.S. sanctions official said on Friday.
Sigal Mandelker, under-secretary of the Treasury for Terrorism and Financial Intelligence, told reporters in Singapore that the United States had placed additional “intense pressure” on Iran this week.
Meanwhile, the United States has instructed oil trading houses and refiners to further cut dealings with Venezuela or face sanctions themselves, even if the trades are not prohibited by published U.S. sanctions, three sources familiar with the matter said.
“With U.S. sanctions taking Iranian and Venezuelan oil off the market, at the same time OPEC and non-OPEC producers want to see higher prices and are currently reluctant to make up for any lost volume,” said Andrew Lipow, president of Lipow Oil Associates in Houston.
Also lifting prices this year has been a deal between the Organization of the Petroleum Exporting Countries and allies such as Russia to cut output by around 1.2 million barrels per day, which officially started in January.
The producer countries are to meet in June, but some cracks are emerging. OPEC leader Saudi Arabia is struggling to convince Russia to stay much longer in the pact, and Moscow may agree only to a three-month extension, three sources familiar with the matter said.
The market has also been supported by slower output growth in the United States, where production has steadied since mid-February. The U.S. government reported on Friday that domestic output in the world’s top crude producer edged lower in January to 11.87 million bpd.
U.S. energy firms this week reduced the number of oil rigs operating to their lowest in nearly a year, cutting the most rigs in a quarter in three years, General Electric Co’s GE.N Baker Hughes energy services firm said.
Futures have been pressured by concerns that a slowing global economy could hit energy demand.
U.S. consumer spending rebounded less than expected in January and incomes rose modestly in February.
Elsewhere, three of China’s top state-controlled bank posted their weakest quarterly profit growth in more than two years.
Still, Barclays bank forecast oil prices “are likely to move still higher in Q2 and average $73 per barrel ($65 WTI), and $70 for the year.”
A monthly Reuters survey of economists and analysts forecast Brent would average $67.12 a barrel in 2019, about 1 percent higher than the previous poll’s $66.44.
Reporting by Stephanie Kelly; additional reporting by Ahmad Ghaddar in London and Henning Gloystein in Singapore; Editing by Marguerita Choy, Louise Heavens and David Gregorio