KYIV -- Ukraine's military says Russia-backed separatists have breached a cease-fire in eastern Ukraine shortly after it went into effect -- a claim rejected by the separatists.

The cease-fire, which entered into force on July 27, had been agreed to last week by negotiators from Ukraine, Russia, and the Organization for Security and Cooperation in Europe (OSCE).

However, separatists violated the new truce near the town of Uzhivka, south of their stronghold city of Donetsk, and around Novomykhaylivka, southwest of Donetsk, according to Ukraine's military.

It said no casualties were reported despite attacks with small arms, grenade launchers, and heavy machine guns.

Ukraine's military insisted that it was continuing to observe the cease-fire.

Separatists in Donetsk rejected Kyiv's accusation, saying they were strictly following their commitments in the truce.

There have been more than 20 cease-fire attempts since the conflict in Ukraine's eastern regions of Donetsk and Luhansk erupted in 2014.

In Kyiv, several hundred people gathered on the evening of July 27 for a protest rally against the new cease-fire.

"We will not disarm our army and turn our soldiers into helpless targets. Our army protects us every day. Therefore, our duty is to support our army," the organizers said.

Kremlin spokesman Dmitry Peskov described the truce as "a significant step toward strengthening mutual trust and defusing tensions" and called on the parties to "fully adhere to their obligations and agreements."

Hours before the truce took effect, Ukrainian President Volodymyr Zelenskiy and his Russian counterpart, Vladimir Putin, discussed the conflict in a phone call and expressed support for the cease-fire.

Zelenskiy's office said that if upheld, the truce would "pave the way for implementing other clauses" of the Minsk accords aimed at putting an end to the fighting in Donetsk and Luhansk.

The Ukrainian president told Putin in the call that further steps were needed to free Ukrainian citizens being held in eastern Ukraine, Crimea, and Russia, it said.

The Kremlin said Putin told Zelenskiy that Ukraine's decision to hold regional elections in 2020 contradicted the Minsk peace deals.

Zelenskiy was elected last year on promises to end the conflict.

Germany and France have mediated between Ukraine and Russia since a peace agreement was signed in the Belarusian capital, Minsk, in 2015, but efforts at implementation have faltered.

The leaders of the four countries met at a summit in Paris in December 2019 to revive the peace process, leading to Kyiv and Russia-backed separatists in the east of Ukraine conducting a series of prisoner exchanges.

Lingering issues remain over a timeline for local elections, control over borders in the separatist-controlled regions, the withdrawal of Russian military units and equipment, and disarmament of separatist groups.

Moscow denies it has troops in eastern Ukraine.

Ukraine's relationship with Russia has been tense ever since protests in Kyiv led to the overthrow of pro-Russian leader Viktor Yanukovych in February 2014.

Russia annexed Ukraine's Crimean Peninsula shortly thereafter and backed separatist forces in eastern Ukraine, sparking a war that has resulted in some 13,200 deaths.

With reporting by AFP, dpa, UNIAN, Reuters, Interfax, and TASS