Lithuania on Monday expanded restrictions on trade through its territory to Russia's Baltic exclave of Kaliningrad, as phase-ins on earlier-announced European Union sanctions against Moscow took effect.

Additional goods barred from Monday morning include concrete, wood, alcohol and alcohol-based industrial chemicals, a spokesperson for Lithuanian customs said.

Russia warned Lithuania and the European Union on Friday that it could adopt "harsh measures" against them if the transit of some goods to and from Kaliningrad did not resume "within the coming days."

The trade curbs have been upgraded as governments, markets and companies worry that Russia could choose to extend the shut-off of the biggest single pipeline carrying Russian gas to Germany beyond a planned 10-day maintenance period.

Kaliningrad borders NATO and European Union states Lithuania and Poland and relies on railways and roads through Lithuania for most goods. The coastal territory has been cut off from some freight transport from mainland Russia since June 17 under EU sanctions imposed over Russia's invasion of Ukraine.

Goods that fall within humanitarian or essential categories, such as food, are exempted from the sanctions.

The row over Kaliningrad's isolation is testing Europe's resolve to enforce the sanctions, raising fears of an escalating confrontation with Russia after other restrictions pushed Moscow to default on its debt.

European officials, with the backing of Germany, sought in late June a compromise to resolve the stand-off. However, sources told Reuters that Lithuania, a former Soviet republic once under Russian domination, had serious reservations about making what could be seen as a concession to Moscow.