(CNN) -- Sri Lankan government soldiers seized the last remaining coastal stretch under the control of Tamil Tiger rebels, the government's Ministry of Defense said.
A photo supplied by a humanitarian group on Sunday shows civilians allegedly injured in government shelling.
The seizure marks the total capture of coastline territory previously controlled by the rebels, the government said Friday -- suggesting the final blow in a quarter-century-long fight.
In a rapid military push, Sri Lankan forces had squeezed Tamil Tiger fighters into approximately 1.5 square miles (four square kilometers) of coastal land.
The chunk of land, known as the no-fire zone or civilian safety area, was under siege by government forces Friday, according to TamilNet, a rebel Web site.
"The entire safety zone area is in smoke ... as shelling by the Sri Lanka army was destroying all the structures within a narrow strip of coastal land, which is densely populated with tens of thousands of people," TamilNet said.
The United Nations estimates that more than 50,000 civilians are trapped there. Watch iReporter Thileepan's footage of the "safe zone" »
"The government is moving forward in extremely difficult circumstances. After all, the ... Tamil Tigers are seeded amidst the middle of all these civilians. It's very difficult to weed out and identify who is a fighter and who is not," said Gordon Weiss, a U.N. spokesman.
"It makes it very very dangerous for civilians, and it explains the very large toll on civilian life that we've seen at this point."
Weiss called the fighting a "bloodbath" at the beginning of the week.
Humanitarian aid groups have reported mass civilian casualties in the fighting.
The situation had worsened by Friday, the International Committee of the Red Cross said. It suspended evacuation and medical rescue operations in the no-fire zone. Aid agencies had been stuck offshore, unable to deliver badly needed relief supplies and evacuate civilians.
"Our staff are witnessing an unimaginable humanitarian catastrophe," said Pierre Krahenbuhl, the ICRC's director of operations. "No humanitarian organization can help them in the current circumstances. People are left to their own devices."
The U.N. Security Council and U.S. President Barack Obama on Wednesday called for both sides to protect civilians and allow humanitarian aid into the conflict zone.
In a statement at the White House, Obama urged Sri Lankan government troops to halt the "indiscriminate" shelling of civilians trapped with the remnants of the country's Tamil Tigers. He also prodded the rebels to stop using civilians as human shields.
Security Council members issued a statement demanding "that all parties respect their obligations under international humanitarian law."
A Red Cross worker was killed Wednesday during shelling in the conflict zone in Sri Lanka -- the third aid worker killed in six weeks -- the Red Cross said.
As many as 70,000 people have been killed since the civil war began.