A bipartisan group of senators demanding an end to US military involvement in Afghanistan urged President Barack Obama on Thursday to seek congressional approval if he wants to keep troops there beyond 2014.

The Obama administration is negotiating a bilateral security agreement with Afghan President Hamid Karzai that could keep troops in Afghanistan after the longest war in US history winds down at the end of this year, when the NATO mission ends.

"We are introducing a bipartisan resolution to say before any American soldier, sailor, airman or Marine is committed to stay in Afghanistan after 2014, Congress should vote," Democratic Senator Jeff Merkley told reporters.

"Automatic renewal is fine for Netflix and gym memberships, but it isn't the right approach when it comes to war."

Conservative Senator Mike Lee and fellow Republican Senator Rand Paul have also signed on.

The resolution does not take sides on keeping troops in Afghanistan, nor does it prevent the US military from attacking Al-Qaeda or gathering intelligence there, Lee noted.

It simply states that "after more than a decade of war, Congress, and more importantly the American people, need to have a voice in this debate," he said.

"The decision to sacrifice American blood and treasure in this conflict should not be made by the White House and the Pentagon alone."

Congressional resolutions are not legally binding, but they can convey a sense of where lawmakers stand on an issue and put some pressure on the administration.

The Senate and House of Representatives both introduced similar measures last year, albeit in amendment form, but neither passed the full Congress.

The Afghanistan war, which began shortly after the 9/11 attacks of 2001, has cost more than 2,300 American lives and $600 billion, the resolution states, adding it is time for Afghans to take responsibility for governing themselves.

"This resolution basically says it all: rebuild America, not Afghanistan," said Senator Joe Manchin, a Democratic co-sponsor who said Karzai was no Washington ally.

"If military might or money would change that part of the world, we'd have changed it by now," Manchin said.

"We haven't been successful."

Afghans elect a new president in April. Some US lawmakers encourage Washington to wait Karzai out, then sign a security pact with his successor.

[Image via CBS News]