May 20 (Reuters) - Grades eased on Wednesday on the first full day of volatile cash roll trading period and as traders watched for updates on the Iran crisis after U.S. President Donald Trump said that negotiations with Iran were in the final stages.

Trump said negotiations with Iran were in the final stages but warned of further attacks unless Iran agreed to a deal. Iranian foreign ministry spokesperson Esmaeil Baghaei said Iran was ready to develop protocols for safe shipping traffic in cooperation with other coastal states, without providing further details.

Traders use the three-day roll period to adjust their crude slates, square up positions and net out exposures following the expiration of the U.S. crude futures contract.

Prices to roll U.S. crude oil futures positions from June to July traded at $3.90 a barrel.

Meanwhile, the U.S. withdrew 17.8 million barrels of crude oil from its inventories, the highest on record, the Energy Information Administration said on Wednesday, as the Iran war has cut global supplies and raised demand for U.S. crude and products.

The country's stock of oil fell to 819.2 million barrels as of May 15, the lowest in 11 months, data showed, on strong refining and export demand.

The spread between WTI and Brent/WTI narrowed for the eight session to last trade at minus $6.76 a barrel, the smallest discount in over a month.

• Light Louisiana Sweet for June delivery eased $2 to a midpoint of a $2 premium and was seen bid and offered between a $1.00 and $3.00 a barrel premium to U.S. crude futures CLc1. ​

• Mars Sour eased 50 cents to a midpoint of a $2.50 premium and was seen bid and offered between a $2.25 and $2.75 a barrel premium to U.S. crude futures CLc1. ​

• WTI Midland eased 25 cents to trade flat and was seen bid and offered between a discount of 25 cents​​ and 25-cent a barrel premium to U.S. crude futures CLc1. ​

• West Texas Sour eased $1.40 to a midpoint of a $4.2 discount and was seen bid and offered between a $4.40 and $4.00 a barrel discount to U.S. crude futures CLc1.

• WTI at East Houston , also known as MEH, traded between a discount of 25 cents​​ and 25-cent a barrel premium to U.S. crude futures CLc1.

• ICE Brent July futures LCOc1 fell $6.26 to settle at $105.02 a barrel on Wednesday​.

• WTI July crude CLc1 futures fell $5.89 to settle at $98.26 a barrel on Wednesday​.

• The Brent/WTI spread narrowed 37 cents to last trade at minus $6.76, after hitting a high of minus $6.19 and a low of minus $7.13.