Moscow on Monday accused Washington of stalling on enforcement rules for a ceasefire in war-torn Syria that took effect late last month and warned it could respond to truce violations unilaterally.

“The delay in the entry into force of the rules agreed upon for responding to violations of the ceasefire in Syria is unacceptable,” lieutenant general Sergei Rudskoy said in a statement, accusing Washington of showing “no readiness” to discuss the agreement with Russia.

Rudskoy added that Russia was ready to unilaterally resort to force against ceasefire violators as of Tuesday, claiming the US had not been ready to coordinate a joint response during talks in Amman last week.

The military official said that Moscow would only resort to force “after receiving credible evidence of armed groups’ systematic violations” of the truce.

US State Secretary John Kerry is set to arrive in Moscow this week to discuss the Syria crisis with Russian counterpart Sergei Lavrov, as well as with President Vladimir Putin.

An unprecedented ceasefire negotiated by Russia and the United States has largely held since February 27 but the truce does not apply to jihadists.

Putin last week ordered the surprise withdrawal of the bulk of Russia’s armed forces from Syria, saying Moscow’s task in the war-ravaged country had been “on the whole” completed.

Moscow is maintaining some troops in Syria to help monitor the progress of a ceasefire in the war-torn country, the Kremlin has said.

The Russian pullout was hailed by the UN envoy for Syria as a “significant development” that could positively influence peace talks.