Russia's foreign minister says opposition groups in Syria failing to respect a truce brokered by Moscow and Washington must be targeted.

Sergey Lavrov said Thursday that it will be "counterproductive" to keep waiting for opposition groups to abide by the cease-fire that went into effect on Feb. 27, adding they must bear full responsibility for violations.

The Islamic State group and al-Qaida's branch in Syria, the Nusra Front, are not covered by the truce. Russia has demanded that other opposition groups, which Washington considers moderate, leave areas controlled by Nusra. Russia set a deadline for Syrian opposition units to withdraw from areas occupied by Nusra, but then agreed to give them more time to pull out.

Despite the truce, fighting has continued to rage in many areas in Syria.