The Sri Lankan government has issued a deadline of noon tomorrow for the Tamil Tigers to surrender. With the embattled rebels unlikely to put down their guns before then, only forceful and immediate international action to halt the fighting can prevent the possible deaths of tens of thousands of civilians trapped between the warring parties.

More than 100,000 men, women and children are trapped in a space roughly the size of Central Park, caught up in a war between the Sri Lankan government and the remaining forces of the separatist Liberation Tigers of Tamil Eelam (LTTE), or Tamil Tigers. Cornered in a shrinking patch of coast in the Northeast of Sri Lanka, with little access to food, water or medicine the past three months, the civilians have remained out of the sight of most of the world. U.N. and humanitarian workers were forced by the government to leave LTTE areas last September; journalists have also been banned from witnessing the unfolding horror.

The area the Sri Lankan government calls the "no fire zone" -- a sea of people, tents, and makeshift shelters on a sliver of jungle and beach -- is being shelled by the military. The Tamil Tigers are using the refugees there as human shields, preventing them from leaving. Available reports suggest 5,000 civilians, including at least 500 children, have died since mid-January, and more than 10,000 have been injured. And even though tens of thousands of civilians escaped the so-called "no fire zone" last night, as the Sri Lankan military advanced, many more remain in grave danger. If the Sri Lankan government's noon deadline passes, the long feared final assault could begin, with innocent civilians suffering disastrous consequences.  

After a 25-year fight against a brutal LTTE insurgency, the government's desire to "finish the job" is understandable. But as the onslaught continues to imperil civilians, an already humiliated Tamil diaspora is growing more volatile, angry, and mobilized -- a potentially explosive combination.

There are disturbing signs that a new generation of young Tamils in the United States, Canada, Britain, Europe, and India are being radicalized. That process has the potential to produce new forms of terrorism and violence. While the Tigers' targets have so far been contained to Sri Lanka, they might soon find new venues. If the Tiger's leadership is removed or killed in a government assault, it's easy to imagine one of the newly energized generation stepping in to fill the void. The dream of an independent Tamil homeland in Sri Lanka resonates powerfully across the diaspora and will certainly live on even after the defeat of the LTTE as a conventional military force. The deaths of tens of thousands of innocent Tamil civilians -- while their family members watch from afar -- is a recipe for another, possibly more explosive, generation of terrorism.

Much of the international community knows what is happening and what is at stake. Nongovernmental organizations, including the International Crisis Group, have been sounding the alarm bells since last fall. Since then, more and more hard proof of unacceptable civilian suffering and war crimes have emerged, including the satellite images of the crowded tent camps seen here, video of dead children, and interviews with exhausted ICRC doctors. Nonetheless, the U.N. and influential governments have been slow to act and have allowed a bad situation to grow much worse.

Similar paralysis and foot dragging by multinational institutions and powerful countries produced Rwanda and Srebrenica. Barack Obama's administration has said it is committed to the principals of international law and humanitarian protection. Sri Lanka is the perfect opportunity for the new U.S. president to show that this is not empty rhetoric.

With both government forces and Tamil Tigers abdicating their responsibility to protect civilians from mass atrocities, urgent, determined, and united international action is necessary to ensure the safety of the innocent -- by the United Nations Security Council, other multilateral organizations, and individual countries that have relations with Sri Lanka, including India and Japan.

The French, British, and U.S. governments released important statements last week calling for a new pause in the fighting. They urged all sides to facilitate humanitarian access and free movement for at-risk civilians. This was a good start, but not nearly enough. Strong and timely messages must continue, and the consequences of a bloody end to this crisis must be made crystal clear. Both Tamil Tiger and government leaders should be told that they are liable to be held personally accountable for breaches of international humanitarian law, and that they need to find a solution that avoids further bloodshed.

Until a more lasting solution can be found and the Tigers persuaded to put down their guns, international actors must demand that the Sri Lankan government halt its offensive. What's needed is a humanitarian pause of at least two weeks to give a chance for relief supplies to get in and civilians to get out. U.N. agencies and the ICRC must be allowed full access to all locations where either civilians or surrendered Tamil Tiger fighters might cross over into government controlled areas. Both civilians -- and disarmed fighters -- need stronger international guarantees of their safety. Only international supervision, unhindered by the government, can provide the necessary level of protection.

All means of influencing the Tamil Tigers must be explored. The Tamil diaspora has an important role in persuading the LTTE to allow the trapped civilians to leave the target area and ultimately, agree to lay down their arms. Simple and one-sided denunciations of government shelling and civilian deaths are not enough -- the Tigers, too, share the blame and must be held accountable.

But at this decisive moment, it is the Sri Lankan government that holds the lives of the trapped Tamil civilians in its hands. It is to the Sri Lankan government that international leaders must send their most immediate messages of restraint. How the war ends will be critical to Sri Lanka's future. Will it be in a bloody massacre whose memory will be used to incite decades more war and terrorism? Or will we see renewed efforts to find a negotiated end to the fighting, and with it, the possibility of building a new, more peaceful Sri Lanka for all its people?