The United States is planning a significant military presence of 13,500 troops in Kuwait to give it the flexibility to respond to sudden conflicts in the region as Iraq adjusts to the withdrawal of American combat forces and the world nervously eyes Iran, according to a congressional report.

The study by the Senate Foreign Relations Committee examined the U.S. relationship with the six nations of the Gulf Cooperation Council - Saudi Arabia, Kuwait, Bahrain, Qatar, the United Arab Emirates and Oman - against a fast-moving backdrop. In just the last two days, Saudi Arabia's ruler named Defense Minister Prince Salman bin Abdul-Aziz as the country's new crown prince after last week's death of Prince Nayef, and Kuwait's government suspended parliament for a month over an internal political feud, AP reports.

The latest developments inject even more uncertainty as the Middle East deals with the demands of the Arab Spring, the end to U.S. combat operations in Iraq at the end of 2011 and fears of Iran's nuclear program.

"Home to more than half of the world's oil reserves and over a third of its natural gas, the stability of the Persian Gulf is critical to the global economy," the report said. "However, the region faces a myriad of political and security challenges, from the Iranian nuclear program to the threat of terrorism to the political crisis in Bahrain."

The report obtained by The Associated Press in advance of Tuesday's release provided precise numbers on U.S. forces in Kuwait, a presence that Pentagon officials have only acknowledged on condition of anonymity. Currently, there are about 15,000 U.S. forces in Kuwait at Camp Arifjan, Ali Al Salem Air Base and Camp Buehring, giving the United States staging hubs, training ranges and locations to provide logistical support. The report said the number of troops is likely to drop to 13,500.

Several members of Congress, most notably Sens. John McCain, R-Ariz., and Lindsey Graham, R-S.C., had pressed for a residual U.S. force to remain in Iraq, but the failure of the two countries to agree on whether American troops should be granted legal immunity scuttled that idea. Instead, officials talked of positioning a strong U.S. force just across the border in Kuwait. The strategy preserves "lily pad" basing that allows the military to move quickly from one location to the next.

As it recalibrates its national security strategy, the United States is drawing down forces in Europe while focusing on other regions, such as the Middle East and Asia. Defense Secretary Leon Panetta has said he envisions about 40,000 troops stationed in the Middle East region after the withdrawal from Iraq. By comparison, a cut of two Army combat brigades and the withdrawal of two other smaller units will leave about 68,000 troops in Europe.

During the 1991 Persian Gulf War, some half a million U.S. forces were in the Middle East region. The United States maintained about 5,000 troops in Kuwait from the end of the Gulf War to March 2003, when U.S. and coalition forces invaded Iraq to topple the regime of Saddam Hussein. The U.S.-led invasion was in response to reports, later discredited, that Iraq was developing weapons of mass destruction.

Senate Foreign Relations Committee Chairman John Kerry, D-Mass., who asked his staff to conduct the study, said in a statement: "This is a period of historic, but turbulent change in the Middle East. We need to be clear-eyed about what these interests are and how best to promote them. This report provides a thoughtful set of recommendations designed to do exactly that."

The 37-page report raises questions about how the United States can leverage its financial aid to force change in the Middle East. Late last year, two Democrats - Sen. Ron Wyden of Oregon and Rep. Jim McGovern of Massachusetts - opposed the U.S. sale of spare parts and equipment to Bahrain, arguing that the ruling Sunni monarchy was violating human rights and using excessive force to crack down on protests. The State Department went ahead earlier this year with the sale of some military equipment, saying it was for Bahrain's external defense and support for the U.S. Navy's 5th Fleet, which is based in the country.

Bahrain stands as a strategic ally to counter Iran.

The report said the Unites States "should not be quick to rescind security assurances or assistance in response to human rights abuses but should evaluate each case on its own merits. U.S. government officials should use these tools to advance human rights through careful diplomacy. ... The United States should make clear that states must not use arms procured from the United States against their own people engaged in peaceful assembly or exploit the U.S. security umbrella as protection for belligerent action against their neighbors."

The report also recommended that the United States promote the development of the Gulf Cooperation Council and the Arab League while strengthening bilateral links to the six countries; seek opportunities for burden-sharing on operations such as missile defense, combat air patrol and maritime security; and push for the integration of Iraq into the Arab fold.

The report emphasized that the region is critical as a counterbalance to Iran, whose conventional military includes 350,000 ground forces, 1,800 tanks and more than 300 fighter aircraft. It also has ballistic missiles with the range to target regional allies, including Israel.

Meanwhile, two Russian navy ships are completing preparations to sail to Syria with a unit of marines on a mission to protect Russian citizens and the nation's base there, a news report said Monday.

The deployment appears to reflect Moscow's growing concern about Syrian President Bashar al-Assad's future.

The Interfax news agency quoted an unidentified Russian navy official as saying the two amphibious landing vessels, Nikolai Filchenkov and Caesar Kunikov, would be heading shortly to the Syrian port of Tartus, but it did not give a precise date.

The official said the ships would carry an unspecified number of marines to protect Russians in Syria and evacuate some equipment from Tartus, if necessary.

Each ship is capable of carrying up to 300 marines and a dozen tanks, according to Russian media reports. That would make it the largest known Russian troop deployment to Syria, signaling that Moscow is becoming increasingly uneasy about Syria's slide toward civil war.

Interfax also quoted a deputy Russian air force chief as saying that Russia would give necessary protection to its citizens in Syria. "We must protect our citizens," Maj. Gen. Vladimir Gradusov was quoted as saying. "We won't abandon the Russians and will evacuate them from the conflict zone, if necessary."

Asked whether the air force would provide air support for the navy squadron, Gradusov said it would act on orders.

The Defense Ministry had no immediate comment, and an official at the Black Sea fleet declined to comment.

Asked if the Pentagon was concerned about the plan, officials in Washington said it depended on the mission. They had no comment on the stated goal of protecting Russian citizens and the Russian military position there, something the United States would do in a foreign country if in a similar situation.

"I think we'd leave it to the Russian Ministry of Defense to speak to their naval movements and their national security decision-making process," said Capt. John Kirby, a Pentagon spokesman, adding that it was not the business of the U.S. Defense Department to "endorse or disapprove of an internal mission like that."

What would greatly concern the United States, he said, is if the Russian naval ships were taking weapons or sending people to support the Assad regime in its crackdown.

"The secretary of defense (Leon Panetta) remains concerned about any efforts by external countries or external organizations to supply lethal arms to the Syrian regime so that they can turn around and use those to kill their own people," Kirby said.

Tartus is Russia's only naval base outside the former Soviet Union, serving Russian navy ships on missions to the Mediterranean and hosting an unspecified number of military personnel.