WASHINGTON (Reuters) - The United States formally complained to China after Chinese nationals pointed lasers at U.S. military aircraft near Djibouti in recent weeks, the Pentagon said on Thursday, an account strongly disputed by China.

Djibouti, on the Horn of Africa, hosts a U.S. military base that is home to about 4,000 personnel, including special operations forces, and is a launch pad for operations in Yemen and Somalia.

The U.S. military has been grappling with lasers being pointed at aircraft for decades. However, the Pentagon accusations highlight the concern the United States has about a Chinese military base just miles from a critical U.S. base in Djibouti.

“They are very serious incidents ... We have formally démarched the Chinese government and we’ve requested the Chinese investigate these incidents,” Pentagon spokeswoman Dana White told reporters.

White said the Pentagon was confident the lasers had been pointed by Chinese nationals and in the past few weeks fewer than 10 incidents had taken place. The intent was unclear.

A U.S. official, speaking on condition of anonymity, said that in one incident last month, two pilots in a C-130 suffered minor eye injuries.

The official said in a few instances, military grade lasers from the Chinese base had been pointed at aircraft.

In a brief statement, China’s Defense Ministry said the U.S. accusations were false.

“We have already refuted the untrue criticisms via official channels. The Chinese side consistently strictly abides by international law and laws of the local country, and is committed to protecting regional security and stability.”

Chinese Foreign Ministry spokeswoman Hua Chunying said the government had conducted “serious checks” and told the U.S. side the accusations were groundless.

“You can remind the relevant U.S. person to keep in mind the truthfulness of what they say, and to not swiftly speculate or make accusations,” she told a daily briefing in Beijing.

Djibouti is strategically located at the southern entrance to the Red Sea on the route to the Suez Canal.

This year, the U.S. military put countering China, along with Russia, at the center of a new national defense strategy.