Lawmakers want the United States to be more aggressive toward China's creation of artificial islands to bolster its claim to much of the South China Sea before it sparks a war in the region.

Countries in the region are alarmed by China's reclamation of some 2,000 acres as part of what one U.S. admiral calls a "Great Wall of Sand" and its construction of an airstrip on a reef in the disputed Spratly Islands. And they are looking to Washington to help stop it.

Administration officials told the Senate Foreign Relations Committee on Wednesday that their diplomatic efforts to contain China's ambitions in the South China Sea and the East China Sea to the north were paying off, but lawmakers were skeptical.

"Diplomacy only works when people see there's a real price to pay. I don't see any price being paid at all," said Chairman Bob Corker, R-Tenn.

"It seems like we're letting certain things go unchallenged," added Sen. Ben Cardin of Maryland, the committee's ranking Democrat.

Wednesday's hearing came a day after The Wall Street Journal reported that Defense Secretary Ashton Carter has asked Pentagon officials for more aggressive options to challenge China's claims, including the use of military aircraft and Navy ships to directly contest them. Meanwhile, Secretary of State John Kerry is expected to raise the issue with Chinese officials during a visit this weekend to Beijing.

David Shear, assistant secretary of defense for Asian and Pacific security affairs, would not confirm the report when asked by lawmakers, but said the Pentagon's position is that U.S. forces are free to navigate through areas Washington considers international waters.

"We're going to continue to exercise that right both on the water and in the air," he said.

China's aggressive actions to claim both water and airspace hundreds of miles from its coast has turned the South China and the East China seas into global flash points and greatly enhanced the risk of war in eastern Asia. Neighboring countries, some of which are key U.S. allies, have pushed back against Beijing's moves, raising the risk that Washington may get dragged into any conflict.

"When one looks at China's pattern of provocative actions towards smaller claimant states — the lack of clarity on its sweeping nine-dash line claim that is inconsistent with international law and the deep asymmetry between China's capabilities and those of its smaller neighbors — well it's no surprise that the scope and pace of building man-made islands raise serious questions about Chinese intentions," Navy Adm. Harry Harris, commander of the U.S. Pacific Fleet, said in a March 31 speech in Australia.

"How China proceeds will be a key indicator of whether the region is heading towards confrontation or cooperation."

Though it may seem Beijing is winning the staring contest, its behavior in the region is driving East Asian countries closer to the United States, said Daniel Russel, assistant secretary of state for East Asian and Pacific Affairs.

"We have become an even more trusted partner as a result of this behavior," Russel said. "They are inviting the United States in. If the Chinese strategy was to freeze us out, it is not working. It has backfired."

A new defense agreement with Japan signed last month commits Tokyo to extend its maritime and missile defense capabilities across the region in exchange for a U.S. commitment to defend its administration of the Senkaku Islands, which also are claimed by China. U.S. officials also are working on a deal that would allow a rotational presence of U.S. troops in the Philippines for the first time in more than two decades.

But the demand for greater U.S. involvement also comes at a price: Despite his vaunted "pivot" to Asia, President Obama has been distracted by other crises, especially in the Middle East and Europe, and regional states perceive that China has benefited from that attention deficit. Nations in the region also are keeping close watch on the debate in Congress over "Fast Track" legislation that is important for the Trans-Pacific Partnership trade deal, a top priority for many Pacific Rim nations.