April 20 (Reuters) - U.S. stock index futures inched lower on Monday after a record rally on Wall Street last week as dimming prospects of an end to the Iran conflict prompted investors to curb their risk appetite.

Iran opened the Strait of Hormuz on Friday, prompting a buying frenzy across markets, with the S&P 500 and the Nasdaq hitting record highs for the third consecutive session. They also marked their biggest weekly jumps since May.

However, Tehran reimposed the closure of the waterway following the escalation in tensions, after the U.S. said it had seized an Iranian cargo ship that tried to run its blockade.

Iran's foreign ministry said on Monday that there were no plans for a second round of negotiations with the U.S., as the blockade undermined the talks and differences over Tehran's nuclear program remained.

Oil prices jumped 5% on Monday, with U.S. energy stocks higher in premarket trading. Exxon Mobil and Chevron gained 2% and 1.9%, respectively, and Occidental Petroleum added 2.5%.

"Near-term escalation to gain an upper hand in negotiations cannot be ruled out," said Mohit Kumar, an economist at Jefferies.

"Our view remains that we are moving towards a deal. We are at a stage where it is not in the interest of either party to carry on with the war. The MAGA base of Trump does not want to continue, and Trump wants a deal. For IRGC, the objective is survival."

At 04:50 a.m. ET, Dow E-minis were down 303 points, or 0.61%, S&P 500 E-minis were down 35.75 points, or 0.50%, and Nasdaq 100 E-minis were down 140.5 points, or 0.52%.

The CBOE Volatility Index, known as Wall Street's "fear gauge", gained after falling for the last eight sessions and was last up 2.25 points at 19.73, a one-week high.

Futures tracking the small-cap Russell 2000 index slipped 0.9% after the index notched a record high on Friday.

Quarterly earnings will be in focus as investors wait to assess the impact of the Iran war on corporate results and its fallout on the broader economy.

Defense giants Lockheed Martin and RTX, alongside tech stocks such as IBM and ServiceNow, are scheduled to report later this week. Tesla will kick off results from the so-called "Magnificent Seven" cohort on Wednesday.

Among premarket movers, Marvell Technology advanced 6% after The Information reported on Sunday that Alphabet's Google is in talks with the chipmaker to develop two new chips to run AI models more efficiently.

QXO shares dipped 3.6% after the construction supplies distributor struck a $17 billion deal on Sunday to acquire building products distributor and installer TopBuild.

(Reporting by Purvi Agarwal in Bengaluru; Editing by Anil D'Silva)