By Kristin Roberts

WASHINGTON, July 11 (Reuters) - The United States has failed to stop Kurdish militants inside Iraq from launching strikes against Turkey, and Ankara is nearly out of patience, Turkey's ambassador in Washington warned on Wednesday.

Ambassador Nabi Sensoy said Turkey would not rule out military action inside Iraq, reiterating statements from other senior Turkish officials.

He said Washington has not used its influence with either the Iraqi central government or Kurdish allies to stop militant activity on the Turkish border, and suggested that U.S. arms were being used by the militants attacking Turkey.

"We know that the United States is supplying arms to the northern Iraqi administration and it is just possible that they have been ending up in the hands of the terrorist organization," Sensoy told reporters.

He stressed he did not believe the United States is funneling weapons to the outlawed Kurdistan Workers Party (PKK) militants who are using Iraq's autonomous Kurdistan region as a springboard for attacks on Turkey.

But he accused Kurdistan President Masoud Barzani of actively supporting the PKK, which is labeled a terrorist group by both Turkey and the United States, but not Iraq.

He said Barzani was giving the PKK safe haven, food, weapons and equipment.

"I think the Turkish people have shown enough patience. The Turkish government has shown not only patience but enough restraint as far as I can see," the ambassador said.

Sensoy's comments come as Turkey builds up its forces along its border with Iraq. Iraq's foreign minister on Monday said the Turkish army had 140,000 soldiers at the border.

The Pentagon has dismissed that estimate, but will not say how many troops Turkey has massed there. Sensoy also would not comment on troop levels along the border.

But he said troop levels were a response to PKK activity.

"We should see the movement of the Turkish troops in the southeast of the country along the Iraqi border in the light of all these developments in the past. It is part of our struggle, continuous struggle, with the terrorist organization."

Tensions have soared along the mountainous border region following an upsurge in attacks across Turkey that Ankara blames on PKK militants.

The Pentagon stresses that Turkish military intervention inside Iraq would not be "helpful," but has otherwise repeatedly refused to discuss the volatile situation.

U.S. and Iraqi forces are already stretched fighting insurgents elsewhere and cannot spare troops to tackle the PKK in what is a relatively peaceful region of Iraq, according to U.S. officials.

Given that, Sensoy indicated Washington should not criticize Turkey's desire to defend itself.

"If the United States government, administration, feels itself to have the right to intervene in Iraq in order to protect itself from terrorists, then Turkey should be able to protect its people and its country from the threat and the actual activities of a terrorist organization at our doorstep."

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