April 14 (Reuters) - Grades were mixed on Monday, dealers said, as a key pipeline that moves crude from Alberta to U.S. refineries in Illinois, Oklahoma and along the U.S. Gulf Coast remained offline.

Pipeline operator South Bow SOBO.TO said it is keeping an eye on inclement weather before proceeding with a planned controlled restart of its Keystone oil pipeline system.

The Calgary-based company had previously indicated it was targeting Tuesday for full service restoration on the Keystone pipeline, which has been shut down since last Tuesday following an oil spill near Fort Ransom, North Dakota.

Some U.S. refiners, especially in the Midwest, rely heavily on the type of oil produced in Canada and delivered by Keystone.

Elsewhere, Kazakhstan's oil output fell in the first two weeks of April by 3% from the March average, the energy ministry said on Monday, confirming a Reuters report, but is still above the OPEC+ quota it has pledged to meet after months of overproduction.

* Light Louisiana Sweet WTC-LLS for May delivery rose 3 cents to a midpoint of a $2.23 premium and was seen bid and offered between a $2.15 and $2.30 a barrel premium to U.S. crude futures CLc1

* Mars Sour WTC-MRS rose 30 cents to a midpoint of a $1.30 premium and was seen bid and offered between a $1.20 and $1.40 a barrel premium to U.S. crude futures CLc1

* WTI Midland WTC-WTM was unchanged at a midpoint of a 90-cent premium and was seen bid and offered between a 70-cent and $1.10 a barrel premium to U.S. crude futures CLc1

* West Texas Sour WTC-WTS fell 20 cents to a midpoint of a 10-cent premium and was seen bid and offered between a discount of 10 cents and 30-cent a barrel premium to U.S. crude futures CLc1

* WTI at East Houston WTC-MEH, also known as MEH, traded between a $1.20 and $1.40 a barrel premium to U.S. crude futures CLc1

* ICE Brent June futures LCOc1 rose 12 cents to settle at $64.88 a barrel

* WTI May crude CLc1 futures rose 3 cents to settle at $61.53 a barrel

* The Brent/WTI spread WTCLc1-LCOc1 narrowed 2 cents to last trade at minus $3.84, after hitting a high of minus $3.78 and a low of minus $3.92

(Reporting by Georgina McCartney in Houston; Editing by Nia Williams)

((Georgina.McCartney@tr.com))