PODGORICA, Montenegro (AP) — Clashes erupted on Monday during an opposition protest in Montenegro reflecting a deep political crisis between the pro-Western and pro-Serb and pro-Russian camps in the small Balkan country that is a member of NATO.

Montenegrin police used pepper spray against hundreds of protesters who threw rocks, bottles and other objects during a demonstration outside the parliament, said a police statement. No one was seriously injured, police said.

The protest was held as lawmakers inside the parliament building voted to strip the country’s pro-Western president of a decisive role in appointing the prime minister. The law was pushed forward by the pro-Serb and pro-Russian majority in the parliament, angering the pro-Western opposition.

The disputed law was passed on Monday by 41 lawmakers in the 80-member parliament.

The U.S. embassy in Podgorica called for calm.

“The United States urges an immediate return to a calm and constructive discourse,” the embassy said on Twitter. “We call on all Montenegrin leaders and citizens to keep talking and find peaceful solutions to political problems.”

Montenegro, a key Western ally in the Balkans, has been paralyzed by a months-long government crisis that has stalled the country’s European Union membership integration process. Montenegro’s government fell in a no confidence vote in August and a political stalemate has persisted since then.

Montenegro’s political crisis has sparked concerns of instability as the war rages in Ukraine. Since it became independent in 2006 from much larger Serbia – Russia’s key ally in Europe – Montenegro has remained deeply divided among pro-Western and pro-Serb and pro-Russia groups.

The latest tensions soared after pro-Western President Milo Djukanovic rejected a nomination from the prime minister from the pro-Serb coalition, citing procedural errors and saying early election should be held instead. Djukanovic’s opponents then responded by changing the laws that give him a key role in appointing the PM.

Djukanovic’s Democratic Party of Socialists on Monday described passing of the law in parliament a “constitutional coup” and pledged to continue with the protests. The party said the crisis in Montenegro has been orchestrated from Serbia’s capital Belgrade.