* Futures down: Dow 0.7%, S&P 500 0.73%, Nasdaq 0.85%

* Jefferies dips after posting Q1 profit below estimates

* OECD warns Iran war erases global growth upgrade

* Weekly jobless claims numbers, Fed speakers on deck

(Updates with prices, analyst comment)

By Purvi Agarwal and Twesha Dikshit

March 26 (Reuters) - U.S. stock index futures slipped on

Thursday following gains in the previous session, as investors

remained cautious about developments in the Middle East while

weighing the prospects for de-escalation in the conflict.

U.S. President ​Donald Trump said Iran was desperate to make

a deal to end the fighting, contradicting the Iranian foreign

minister, who said Tehran was reviewing a U.S. proposal but had

​no intention of holding talks to wind down the war.

Contradictory signals from both sides left markets on edge,

as hopes for a breakthrough to restore shipping through the

crucial Strait of Hormuz remained uncertain.

"The relative calm in markets suggests some investor

confidence that hostilities may eventually wind down, however

slim that prospect remains," said Molly Schwartz, cross-asset

macro strategist at Rabobank.

At 6:45 a.m. ET, Dow E-minis were down 325 points,

or 0.7%, S&P 500 E-minis were down 48.75 points, or

0.73% and Nasdaq 100 E-minis were down 206 points, or

0.85%.

Wall Street's main indexes closed higher on Wednesday after

Washington delivered a proposal to Iran through Pakistan, while

comments from Iranian officials suggested Tehran might be open

to diplomatic offers even as it publicly denied any ongoing

negotiations.

"Markets appear to have reached an impasse, with investors

caught between two competing narratives ... this has created a

fragile equilibrium across asset classes, where positioning

reflects caution rather than conviction," said Daniela Hathorn,

senior market analyst at Capital.com.

The escalating conflict in the Middle East has knocked the

global economy off a stronger growth path, the OECD warned on

Thursday, with a closure of the Strait of Hormuz threatening to

push inflation sharply higher.

Central banks have been put in a tough spot with regard to

interest rates, with money market participants no longer pricing

in any easing from the U.S. Federal Reserve this year. Two rate

cuts had been expected before the Iran conflict erupted,

according to the CME Group's FedWatch Tool.

On the data front, investors will parse through weekly

jobless claims data and comments from Federal Reserve officials

Lisa Cook, Stephen Miran, Michael Barr and Philip Jefferson.

Among individual movers, Jefferies Financial ( JEF ) was

down marginally in premarket trading, as the investment bank

missed analysts' estimates for first-quarter profit due to

losses on loans to collapsed companies.

Shares of Olaplex Holdings ( OLPX ) jumped 50% after

Germany's Henkel agreed to buy the hair-care brand in

a $1.4 billion deal.

U.S.-listed shares of gold miners slipped as bullion prices

declined more than 1%. Newmont ( NEM ) slipped 3.1%,

Sibanye Stillwater lost 4.4% and Harmony Gold

shed 4%.