WASHINGTON, Oct. 15 (UPI) -- A $1 billion deal to pipe natural gas to Syria from Iran announced in early October signals increasing ties between the two foes of the United States, and its path through Turkey could inflame tensions at a time when U.S.-Turkish relations are strained.

Iran plans to export about 100 billion cubic feet of natural gas to Syria every year, according to Iranian state-run media. The deal would require the gas to be transported through Turkey by pipeline, a situation that could hurt U.S. efforts to isolate the energy economy of Iran.

But Iran's ability to supply Syria with that much natural gas remains unclear. In the winter of 2006, domestic shortages forced Iran to stop major natural gas shipments to Turkey, causing Ankara to turn to Moscow for supplies. Turkey, which faces its own increasing natural gas demand, has shown interest in investing in Iran's massive South Pars field and has been importing between 100 billion and 150 billion cubic feet of natural gas from Iran since the Iran-Turkey pipeline was built in 2001.

Iran is desperate for investment needed to develop its natural gas reserves, especially the South Pars field in the Persian Gulf, estimated to be home to about 280 trillion cubic feet of natural gas. Under pressure from the United States, and more recently France, many international petroleum companies are hesitant to invest in South Pars development.

Syria holds 8.5 trillion cubic feet of natural gas, and while it is hoping to increase its production, for the time being it uses all of the roughly 250 billion cubic feet it produces annually, according to the Energy Information Administration, the data arm of the U.S. Department of Energy.

Iran sits on the world's second-largest natural gas deposits after Russia, 974 trillion cubic feet, but has the lowest production in the Persian Gulf.

Washington has been unambiguous that it does not support any investment that helps Iran, especially when it comes from allies such as Turkey.

“Undersecretary Burns made clear in his recent visit there, we certainly don't think it's an appropriate moment for any country to be expanding its economic activities in Iran. The international community needs to have full support from all its members to be able to convince Iran to comply with U.N. Security Council resolutions, and we'd certainly like to see Turkey fully cooperating in that regard,” U.S. State Department deputy spokesman Tom Casey said after Nicolas Burns, number two at the State Department, visited Turkey in September.

U.S. relations with Turkey have been under increasing stress in the past week after the Armenian Genocide Resolution, H.R. 116, was introduced in the U.S. House of Representatives. The resolution would officially refer to the deaths of 1.5 million Armenians in Turkey during World War I as a genocide but has faced tremendous opposition from the White House.

Turkey vehemently objects to the description and on Thursday recalled its ambassador to Washington in protest of the congressional action. In order to maintain stable relations with Turkey, U.S. President George W. Bush's administration has been careful to use the term “mass killings” to refer to what many describe as genocide.

However the current tensions with Turkey resolve themselves, Washington is still faced with increased ties between two countries the State Department and President Bush have long criticized for supporting terrorism and human-rights abuses. Both countries have been censured by the United Nations; Iran for its nuclear program and Syria for its violent involvement in Lebanese affairs.

Despite differences in religion -- Syria is a predominantly Sunni country that brands itself secular, while Shiite Iran calls itself an Islamic Republic -- Tehran and Damascus have often found common cause. Syria was one of the few countries to support Iran during the Iran-Iraq War in the 1980s, and Tehran and Damascus have both long supported Hezbollah in southern Lebanon. Each is also very vocal in their opposition to U.S. policy in the Middle East.

While the United States has been critical of Turkey for its energy investments in Iran, Washington has little leverage since the United States depends on Turkey as a critical staging ground for flying supplies into Iraq.

Washington has also been at odds with Ankara over Turkey's desire to send troops into northern Iraq to battle the PKK, a Kurdish insurgent group in eastern Turkey with ties to the Kurds in northern Iraq. The United States has insisted that Turkish troops stay out of Iraq, but Turkey demands that something be done to combat the group as it crosses the border. A PKK attack on Turkish government forces left 13 soldiers dead on Oct. 7.