Mark Esper, the US defence secretary, said Turkey risks “serious consequences” by continuing its offensive against Kurdish-held areas in Syria, which came after Donald Trump withdrew US troops from the border this week.
“The explosion occurred within a few hundred metres of a location outside the Security Mechanism zone and in an area known by the Turks to have US forces present,” Navy Captain Brook DeWalt said in a statement.
“The US demands that Turkey avoid actions that could result in immediate defensive action.”
All US troops were accounted for with no injuries after the incident and US forces have not been withdrawn from Kobane, the spokesperson said.
At least 30 civilians have been killed in Syria since the Turkish 'Operation Peace Spring' began on Wednesday, the UK-based Syrian Observatory for Human Rights reported on Saturday.
Turkey’s Defence Ministry has said US forces were not targeted and it was returning fire from Kurdish fighters that originated near the base close to Kobane.
“The firing was ceased as a result of the issue being relayed to us by the US,” the ministry said.
Top Pentagon officials have stressed the need for Turkey to avoid endangering US forces inside Syria, which numbered about 1,000 before the offensive began.
Although the US does not plan on firing on Turkey, which is a Nato ally, the Pentagon has noted the US troops’ right to defend themselves.
“Everyone is fully aware that we are the United States military. We retain the right of self-defence,” General Mark Milley, the chairman of the Joint Chiefs of Staff, said.
The White House has also threatened to “shut down the Turkish economy” with sanctions over its military action.
Turkey’s offensive began days after Mr Trump spoke with Recep Tayyip Erdogan, the Turkish president, and ordered US troops to withdraw from northern Syria.
"Our position is crystal clear. This incursion is wrong. We want to see maximum restraint, and avoid taking our eye off the ball with Daesh (IS)," Mr Raab said.
"My fear is that the risk is that the humanitarian situation ... could be made worse."
Lord Robertson, a former UK defence secretary and secretary-general of Nato, has said Mr Trump’s decision showed the importance of Nato and international military alliances.
“At the moment we are in a situation where the Trump administration's capricious way of dealing with foreign policy has led to complete confusion in the world today and has allowed some very bad actors to take centre stage,” Lord Robertson said.
The Trump administration has been accused by Kurdish leaders and US lawmakers of abandoning its allies by withdrawing troops.
Turkey has said its aim is to defeat the Kurdish YPG militia, who have led the fight against Isis in Syria, and said that the military operation will continue.
More than 100,000 people have been forced to flee their homes since the offensive began on Wednesday, according to the UN.
Agencies contributed to this report