BEIRUT (AP) — Clashes have erupted on the Syrian-Iraqi border between Islamic State group militants and Iraqi paramilitary fighters as the extremist group defends its last stronghold in the region, a Syria monitoring group and an Iraqi official said Saturday.

The Britain-based Syrian Observatory for Human Rights said the clashes started late Friday and continued into Saturday. The Observatory said that IS militants inside Syria repelled an attack by Iraq's Popular Mobilization Forces, the paramilitary group of mostly Shiite fighters within the Iraqi security forces. The Observatory said the attack took place near the border town of Boukamal but that the PMF fighters crossed back into Iraq.

Jaafar al-Husseini, spokesman for Iraq's Kataeb Hezbollah, a group within the PMF, told The Associated Press his forces clashed with IS just meters from the border with Syria. He said his forces also fired rockets inside Syria from Qaim, the Iraqi border town reclaimed from IS Friday.

But al-Husseini said his fighters didn't cross into Syria. He said forces from Iraqi militias were already fighting in Syria alongside the Syrian government and other Iran-supported militias to reclaim the last stronghold of the group and secure the road between Iraq and Syria, all the way to Lebanon.

He said his forces are building berms along the border to prevent militants from sneaking back.

On Friday, Syrian President Bashar Assad's military announced the capture of the eastern Syrian city of Deir el-Zour, while Iraqi Prime Minister Haider al-Abadi proclaimed victory in retaking the town of Qaim on the border, the militants' last significant urban area in Iraq. The Syrian forces are expected to now focus on Boukamal.

Boukamal is the last urban center for the militants in both Iraq and Syria where Syrian troops —backed by Russia and Iranian-supported militias — and U.S.-backed Syrian Democratic Forces are vying for control of the strategic border town, key to control of the borders between the two countries.

Washington is wary of increasing Iran influence in the area and has backed the SDF in their bid to uproot IS from the borders with Iraq. The proximity of forces in the area has raised concerns about potential clashes between them as they approach Boukamal from opposite sides of the Euphrates River, and now from across the border with Iraq.

Al-Husseini said the PMF will participate in the liberation of Boukamal and will head north to protect the borders and secure the road from Iran to Lebanon.

"We can say after liberating the borders that we have foiled the U.S. project on the Iraq and Syrian borders," said al-Husseini.

Spokesman for the U.S. coalition Col. Ryan Dillon told AP that despite multiple forces operating in the area, including the Syrian troops, Russia and Iranian-backed militias, the coalition continues to de-conflict with the Russians to avoid confrontation.

Dillon said there are between 2,500 and 3,500 remaining IS fighters concentrated around Boukamal.

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Abdul-Zahra reported from Baghdad.