Oil prices rose on Monday, climbing towards their highest levels in more than seven years on fears that a possible invasion of Ukraine by Russia could trigger sanctions from U.S. and Europe and disrupt energy exports from the world's top producer.

Brent crude futures was at $95.73 a barrel by 0109 GMT, up $1.29, or 1.4%, after earlier hitting an intraday high of $95.91. U.S. West Texas Intermediate (WTI) crude rose $1.49, or 1.6%, to $94.59 a barrel, hovering near a session-high of $94.92.

Comments from the United States about an imminent attack by Russia on Ukraine have rattled global financial markets.

Russia could invade Ukraine at any time and might create a surprise pretext for an attack, the United States said on Sunday.

"If ... troop movement happens, Brent crude won't have any trouble rallying above the $100 level," OANDA analyst Edward Moya said in a note.

"Oil prices will remain extremely volatile and sensitive to incremental updates regarding the Ukraine situation."

Investors are also watching talks between the United States and Iran to revive the 2015 nuclear deal.

However, a senior Iranian security official said on Monday that progress in talks was becoming "more difficult."

In the United States, the robust oil prices are encouraging energy firms to ramp up output as they added the most oil rigs in four years last week, energy services firm Baker Hughes Co said on Friday.