By Cassie Werber 

LONDON--Brent crude oil fell to its lowest point in over two weeks Thursday, as the strength of the U.S. dollar weighed on prices and sanctions on Russia made some investors wary of entering the market.

ICE September crude was down 0.68% at $105.79 a barrel. It last fell this low on July 15, which followed a slide downward from highs associated with a violent insurgency in Iraq.

WTI crude on the Nymex exchange was down 0.88% at $99.39 a barrel, also the lowest since July 15.

A relatively strong dollar may be behind some of the recent weakness seen in crude prices, JBC Energy, an energy-information provider, wrote in a note to clients. A strong dollar weakens buying appetite because crude is priced in dollars, and becomes more expensive to the rest of the world when the U.S. currency strengthens.

The U.S. Dollar Index has moved higher by about 2% since July 10, JBC said, while "further gains could be seen as recent U.S. economic data showed a strong rebound in GDP growth, thereby implicitly increasing the chances for timelier monetary tightening and consequently higher interest rates."

The move lower came despite rising tension between western economies and Russia, JBC said.

Markets may be in wait-and-see mode, said Thina Saltvedt, senior oil market analyst at Nordea Bank, adding that many in the market are trying to work out why prices are down, rather than reflecting any risk associated with Russia by rising.

"Investors are a bit skeptical of all kinds of risky assets because they don't know how Russia will react to the sanctions," she said.

The risk of Argentina defaulting on its debts may also be adding some hesitation to general market sentiment.

"Investors are waiting to see who will save Argentina, who will restructure their debt so that they can get back on their feet," said Ms. Saltvedt.

Recently the ICE's gas oil contract for August delivery was down $9.50 at $883.75 a metric ton, while Nymex gasoline for September delivery was down 275 points at $2.7883 a gallon.

Write to Cassie Werber at cassie.werber@wsj.com<mailto:cassie.werber@wsj.com>