Trump said in a Twitter post on Thursday: "We have one of three choices: Send in thousands of troops and win Militarily, hit Turkey very hard Financially and with Sanctions, or mediate a deal between Turkey and the Kurds!". The figure could not be independently verified.
North Atlantic Treaty Organisation member Turkey considers the Syrian Kurdish fighters to be terrorists linked to a Kurdish insurgency inside Turkey and says the offensive is a counterterrorism operation necessary for its own national security.
Turkish officials said the Kurdish militia has fired dozens of mortars into Turkish border towns the past two days, including Akcakale, killing at least six civilians, including a 9-month-old boy and three girls under 15.
The Turkish Defense Ministry said the offensive was progressing "successfully as planned". The village, Dedat, was later captured by the Turkey-backed rebels, according to the agency. But it was not possible to confirm that death toll, and the Kurdish-led Syrian Democratic Forces, which are allied with the United States, said they could not provide a count of their own. But their claims could not be independently verified.
The Kurdish officials said Turkish shells fell near another prison facility on Friday and Wednesday in Qamishli, which is only 2 miles (3 kilometers) from the Turkish border.
The word betrayal is doing the rounds as Kurdish fighters proved pivotal in the fight against the Islamic State group.
"These people are already under extreme duress", he says.
The Kurdish-led force said 22 of its fighters were killed since Wednesday.
In a separate statement, US Ambassador to the UN Kelly Craft said that if Turkey does not "protect vulnerable populations" or does not guarantee that the Islamic State (IS) jihadist group "cannot exploit these actions to reconstitute", there will be consequences.
United States ambassador to the UN Kelly Craft said: "Failure to play by the rules, to protect vulnerable populations, cannot be expected to restore these actions, will have consequences".
The monitor said four civilians were killed in Tal Abyad when an air strike hit the vehicle in which they were fleeing the fighting, while another three were shot dead by snipers around the border town.
Despite the criticism, Turkish President Recep Tayyip Erdogan said his country "will not take a step back" from its offensive.
Erdogan has asked European Union to instead increase its support, and has threatened to open the doors to Europe for Syrians if the request is declined.
The ministry's statement comes after shelling from the militia into Turkey and Turkish military strikes in northern Syria, with casualties on both sides.
Although U.S. troops in the region have been withdrawn on order of President Donald Trump, Esper said there was still the possibility that "Turkey's actions could harm U.S. personnel in Syria".
Fighting mostly centred around Tal Abyad - one of the main Kurdish-controlled towns in the area coveted by Ankara.
The claims from the SDF will no doubt fuel fears from USA officials that the Turkish invasion of Syria could lead to the thousands of ISIS prisoners under Kurdish watch being freed.
The Turkish government says millions of refugees now in Turkey will be settled in the safe zone, while Kurdish leaders say only refugees originally from that part of Syria will be allowed to return, if they control the area.
The proposed security strip, 20 miles deep, would span across most of Syria's multi-ethnic northern border areas and rival administrations created by almost nine years of civil war. Ankara wants to settle 2 million Syrian refugees, mainly Arabs, in the zone.