* Iran deal to take effect Jan. 20
* Obama urges Congress not to impose new sanctions on Iran
* North Sea Buzzard oilfield ramping up after problems
(Rewrites top, adds analyst's quote, updates prices, changes byline/dateline, pvs LONDON)
NEW YORK, Jan 13 (Reuters) - Brent oil fell on Monday as the market absorbed news of a deal between Western nations and Iran to curb its nuclear program and the resumption of production from a key North Sea oilfield.
U.S. oil fell by more than $1, then pared some losses, though continued to be pressured by poor U.S. jobs data that suggested an economic recovery in the world's largest oil consumer may be faltering.
The sharper drop in the U.S. benchmark sent Brent's premium to U.S. oil to more than $15 for the second time in six weeks.
"Those Friday employment numbers were really ugly and it has us thinking, 'Gee things aren't as good as we think they are,"' said Bill O'Grady, chief market strategist at Confluence Investment Management in St. Louis.
Brent crude for February delivery fell 30 cents to $106.95 per barrel by 11:51 a.m. EST (1651 GMT). The contract had settled 86 cents higher on Friday. U.S. crude slipped 75 cents to $91.97 per barrel, after closing $1.06 higher on Friday.
Brent's premium to U.S. oil <CL-LCO1=R> last stood at $14.92 after widening by nearly $1 to $15.51 per barrel.
The deal between Iran and six major powers intended to pave the way for a solution to a long standoff over Tehran's nuclear ambitions will come into force on Jan. 20, the Iranian Foreign Ministry and the European Union said on Sunday.
Sanctions against Iran over its nuclear program have kept about 1 million barrels per day of oil off global markets. Some sanctions relief would start on the first day of the six-month agreement's implementation on Jan. 20 and some will be withheld until its final day, senior U.S. officials said.
Still, murmurings of discord rumble under the surface of the deal. U.S. President Barack Obama urged Congress not to impose additional sanctions on Iran, while the ruler of Dubai said the international community should ease sanctions on the Islamic Republic.
The West's deal with Iran could cause further rifts between two Muslim sects and eventually destabilize the region and threaten supply, O'Grady said. Iran is a Shi'ite republic and Sunnis dominate Saudi Arabia.
"I do think that people in the market are beginning to realize a nuclear deal in Iran doesn't ease tensions, in fact it may raise them," he said. "That sentiment is starting to steadily seep into the market and as it does it should have a significant impact on the Brent/WTI spread."
Meanwhile, losses in Brent were capped by some supply constraints. Buyers of Iraq's Basra Light oil will see a reduction in February volumes, trade sources said, an early setback in Iraq's plans to boost exports this year.
A partial end to supply disruption from Libya has also pressured Brent since the start of January.
Libya's El Sharara field is producing 300,000 barrels per day of oil compared to its peak output of about 340,000 bpd, Oil Minister Abdelbari Arusi said on Sunday.
Brent oil also came under pressure as operator Nexen confirmed the North Sea's Buzzard oilfield was ramping back up to full production after output problems last week.
Buzzard is the largest of the fields that contribute to the Forties blend, the most important of the North Sea crudes underpinning the Brent benchmark.
In the U.S., the market awaited oil inventory data on Tuesday and Wednesday to gauge supply. Last week oil inventories showed a sixth straight decline while diesel and gasoline stocks rose more than expected.
(Additional reporting by Simon Falush in London and Jacob Gronholt-Pedersen in Singapore; Editing by William Hardy, Dale Hudson and Meredith Mazzilli)