ANKARA/BEIRUT (Reuters) - Turkish forces shelled a Kurdish-controlled area of northern Syria, killing four Kurdish militants, Turkish state broadcaster TRT said on Wednesday, and Kurdish-led forces said they responded to Turkish attacks by hitting a Turkish army vehicle.

The Kurdish-led Syrian Democratic Forces (SDF) said the Turkish attacks had led to a temporary halt in the U.S.-backed campaign it is waging against Islamic State (IS) near the Iraqi border.

Turkey has repeatedly warned it would launch a cross-border offensive against the Kurdish YPG militia east of the Euphrates River in Syria, if the U.S. military which supports the Kurdish fighters does not ensure their withdrawal.

The SDF, including the YPG, is the main U.S. partner in the fight against IS in Syria and controls a swathe of the north and east - the biggest chunk of the country after the area held by the Syrian government of President Bashar al-Assad.

U.S. State Department spokesman Robert Palladino said American officials had contacted Turkey and the Syrian Defense Forces to “emphasize the need to de-escalate the situation.”

“Unilateral military strikes into northwest Syria by any party, particularly as American personnel may be present or in the vicinity, are of great concern to us,” he said, calling for coordination between Turkey and the United States and adding that Washington was fully committed to Turkey’s border security.

TRT said barrages of howitzer shells were launched at the Ayn al-Arab, or Kobani region, from Turkey’s southeastern province of Sanliurfa, along the Syrian border. Four militants were killed and six wounded in the strikes on the region.

The SDF, in a statement, said Turkish forces were attacking its positions along the length of the border. SDF forces had responded by destroying a Turkish military vehicle, it said, without giving the location. The SDF reserved the “right to respond to all kinds of attacks.”

The SDF general command said in a separate statement that the Turkish attacks had led to the temporary halt of the campaign it is waging against Islamic State in the Deir al-Zor region.

“The continuation of these attacks will cause a long halt in our military campaign against (Islamic State),” it said.

“We call on the international coalition to show a firm position to deter Turkey from these attacks,” the SDF said.

On Tuesday, President Tayyip Erdogan vowed to crush Syrian Kurdish fighters east of the Euphrates River in Syria - the area where Ayn al Arab, or Kobani, is located.

Over the past two years, Turkish forces have already swept into Syria to push YPG fighters out of territory west of the Euphrates in two separate military campaigns.

Past offensives halted at the banks of the river, in part to avoid direct confrontation with the United States, which has troops alongside the Kurdish fighters further east.

But Erdogan said Turkey was now prepared to press on, issuing what he said was a “final warning” last week to those who would endanger Turkey’s borders.

He said Turkey would focus its attention east of the Euphrates, rather than the city of Manbij where Turkish and U.S. forces agreed in June to carry out joint patrols.

Turkish forces had bombarded YPG positions on Sunday on the eastern shore of the Euphrates river, Anadolu said.