(Adds Foreign Minister Gul, paragraph 4)

ANKARA, May 28 (Reuters) - Two U.S. warplanes briefly violated Turkish airspace near Iraq last week, the military General Staff said on its Web site.

The incident comes amid mounting speculation over a possible Turkish troop incursion into Kurdish northern Iraq to crush Turkish Kurd rebels hiding there. Washington has repeatedly cautioned Turkey, a NATO ally, against making such an incursion.

"Two F-16s belonging to the United States violated Turkish airspace in the southeast region of Anatolia for a period of four minutes (on May 24)," the General Staff said.

Foreign Minister Abdullah Gul played down the incident on Monday, describing it as a "routine matter". He said his ministry was still awaiting more details from the General Staff.

Kathryn Schalow, spokeswoman for the U.S. embassy in Ankara, said: "It seems to have been an accident. An investigation has been opened on the matter."

Turkish newspapers said the airspace infringement may have been intended as a message to Turkey not to send troops into Iraq against rebels of the banned Kurdistan Workers Party (PKK).

The top-selling Hurriyet daily described the incident as "a challenge" that showed U.S. forces were closely monitoring Turkish troop movements along the Iraqi border.

Ankara has long urged U.S. and Iraqi government forces to crack down on an estimated 4,000 PKK guerrillas who use the mountains of mainly Kurdish northern Iraq as a base to direct attacks on military and civilian targets inside Turkey.

Last Tuesday, a suicide bomber killed six people in Ankara in an attack blamed by Turkish authorities on the PKK. The group denied responsibility. The attack has added to political tensions in Turkey as it gears up for July general elections.

On Sunday, Baghdad urged Turkey to pursue only diplomatic means to combat the PKK guerrillas operating out of Iraq.

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