CEYLANPINAR, Turkey (AP) Turkeys military said it captured a key Syrian border town under heavy bombardment Saturday as its offensive against Kurdish fighters pressed into its fourth day with little sign of relenting despite mounting international criticism.

Turkish troops entered central Ras al-Ayn according to Turkeys Defense Ministry and a war monitor group, marking the most significant gain since the invasion began Wednesday. The ministry tweeted: Ras al-Ayns residential center has been taken under control through the successful operations in the east of Euphrates river.

Turkeys continued push into Syria comes days after U.S. President Donald Trump cleared the way for Turkeys air and ground offensive, pulling back U.S. forces from the area and saying he wanted to stop getting involved with endless wars. Trumps decision drew swift bipartisan criticism that he was endangering regional stability and risking the lives of Syrian Kurdish allies who brought down the Islamic State group in Syria. The Kurdish-led Syrian Democratic Forces was the main U.S. ally in the fight against the Islamic State group and lost 11,000 fighters in the nearly five-year battle against the extremists.

An Associated Press journalist across the border in Turkey heard the sound of sporadic clashes as Turkish howitzers struck the town and Turkish jets screeched overhead.

Syrian Kurdish forces appeared to be holding out in some areas of the town.

The Kurdish Syrian Democratic Forces released two videos said to be from inside Ras al-Ayn, showing fighters saying that it is Saturday and they are still there.

The fighting was ongoing as the Kurdish fighters sought to reverse the Turkish advance into Ras Al-Ayn, the Syrian Observatory for Human Rights said.

Earlier in the day, Turkish troops moved to seize control of key highways in northeastern Syria, the Turkish military and the Observatory said.

Turkeys state-run Anadolu news agency said that Turkey-backed Syrian opposition forces had taken control of the M-4 highway that connects the towns of Manbij and Qamishli.

The SDF said that Turkish troops and their Syrian allies reached the highway briefly before being pushed back again.

Turkish troops also cut the route linking the northeastern city of Hassakeh with Aleppo, Syrias largest city and once commercial center, according to the Observatory.

Since Wednesday, Turkish troops and Syrian opposition fighters backed by Ankara have been advancing under the cover of airstrikes and artillery shelling, reaching the Manbij-Qamishli road about 30 kilometers (19 miles) south of the Turkish border.

Turkey has said it aims to push back the Syrian Kurdish Peoples Protection Units, or YPG, which it considers terrorists for its links to a decades-long Kurdish insurgency within its own borders. The YPG is a main component of the SDF.

The U.N. estimated the number of displaced at 100,000 since Wednesday, saying that markets, schools and clinics also were closed. Aid agencies have warned of a humanitarian crisis, with nearly a half-million people at risk in northeastern Syria.

Turkish President Recep Tayyip Erdogan said Friday Turkey wont stop until the Syrian Kurdish forces withdraw below a 32 kilometer (20 miles) deep line from the border.

The Turkish military aims to clear Syrian border towns of Kurdish fighters presence, saying they are a national security threat.

A civilian wounded in a mortar strike from Syria the previous day in the Turkish border town of Suruc died, Anadolu news agency also reported Saturday, bringing the civilian death toll to 18 in Turkey. Turkeys interior minister said hundreds of mortars, fired from Syria, have landed in Turkish border towns.

The Observatory that keeps track of Syrias civil war said 74 Kurdish-led SDF fighters have been killed since Wednesday as well as 49 Syrian opposition fighters backed by Tukey in addition to 21 civilians on the Syrian side.

Turkeys defense ministry said it neutralized 415 Syrian Kurdish fighters. The number could not be independently verified. Four Turkish soldiers have been killed since the beginning of the offensive, including two who were killed in Syrias northwest.

Frances leader warned Trump in a phone call that Turkeys military action in northern Syria could lead to a resurgence of Islamic State activity.

President Emmanuel Macron reiterated the need to make the Turkish offensive stop immediately, his office said in a statement Saturday.

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Associated Press writers Zeynep Bilginsoy in Istanbul and Bassem Mroue in Beirut contributed to this report.