WASHINGTON — Efforts to speed up the destruction of Syria’s chemical weapons arsenal could be hampered because of tensions with Russia over Ukraine, US Secretary of State John Kerry admitted Thursday.

About a third of Syria’s toxic arms stockpile has now been removed from the war-torn country, and the rest is under control in 12 different locations, Kerry told US lawmakers.

The challenge is now to remove the remaining weapons to Syria’s main port Latakia so they can be shipped out of the country to be destroyed.

The deal to eliminate Syria’s chemical weapons was hammered out late last year between Kerry and his Russian counterpart Sergei Lavrov in talks in Geneva.

It set out specific deadlines which were enshrined in a UN resolution, committing Syria to ship out most dangerous Category 1 chemicals by December 31 and Category 2 chemicals by February 5, with the entire process to be completed by June 30.

After missing a number of deadlines, Syria has drawn up a new 62-day schedule for the UN watchdog, the Organisation for the Prohibition of Chemical Weapons (OPCW).

Kerry told the Senate appropriations committee that Moscow, which has long-standing ties with Syria, had helped cut back the schedule from an initial 100 days proposed by Damascus to 62.

“We believe that could now be reduced by another 20 to 25 days, and we’d like to see that done,” Kerry said.

“Whether or not we can succeed in getting that done will depend to some degree on the outcome of events that we’re obviously all focused on with respect to Ukraine. My hope is … that events in Ukraine will not interfere.”

Kerry was speaking only hours before he flies to London to meet with Lavrov to discuss the crisis in Ukraine, after Russia poured thousands of troops into its southern Crimea peninsula.

But it is clear that tensions over Ukraine could have a fallout on how Russia and the United States work together on other global issues such as Syria.

“I think Russia maintains a significant interest in not having these chemical weapons loose, not having them fall into the hands of terrorists,” Kerry told lawmakers.