Speaking at a press conference in Washington, Scott McClellan said: "No decision has been made. The situation in Liberia now is dynamic, and we do continue to monitor the events closely."
The Pentagon has mobilised some 4,500 marines for a possible deployment in Liberia, following requests from the United Nations, but President George Bush has yet to order an American troop deployment.
Liberian defense minister, Daniel Chea, said that up to 700 civilians have died in recent days during fighting for the Liberian capital Monrovia between troops loyal to Charles Taylor's government and rebel forces besieging the city.
Both sides have paid lip service towards the idea of a ceasefire signed last month under the auspices of a west African-led peace process, but there is little sign that the four-year-old conflict is abating.
Pressure for cease-fire
Anti-government forces have been ordered to halt their offensive on Monrovia, according to rebel spokesman Kabineh Ja’neh, attending peace talks in Ghana on Tuesday.
But the order has not been implemented as "every time they [rebels] intended to leave an area or do a tactical withdrawal, [President Charles] Taylor's forces opened fire, making the situation very difficult for us," said Ja'neh.
He claimed the call for an end to hostilities was made by rebel leader Liberians United for Reconciliation and Democracy (LURD), Sekou Damate Conneh.
West African peacekeepers will not deploy to Liberia until a stable ceasefire is in place on the ground, Nigerian President Olusegun Obasanjo's spokewoman told journalists on Tuesday.
Lagos says it won't send Nigerian
peacekeepers until there is a
peace to keep
Nigeria is to contribute the bulk of a planned 3,000-strong west African peacekeeping force being set up to help bring an end to fighting in Liberia, and the main combat element in its 1,500 troop vanguard.
But Nigerian spokeswoman Remi Oyo said that fighting must halt before such a force is sent in.
"It doesn't make sense to want to go to get into a jam from the beginning," she told a press conference, as the region's military chiefs met in the Senegalese capital Dakar to discuss arrangements for the mission.
"The idea is that the issue of a multinational force is acceptable to everybody on the ground," she added.
International aid and refugee agencies voiced growing concern about a brutal surge in fighting in recent days, warning that the humanitarian situation was catastrophic.
"The situation is extremely desperate," UN humanitarian coordinator spokesman Daniel Austburger told journalists in Geneva, while a French aid group said in Paris that both the food and the health situation in Monrovia had deteriorated dramatically.
The UN refugee agency said that it had lost contact with many of the 15,000 Sierra Leonean refugees in camps around Monrovia, while refugee evacuations by ship had also ground to a halt because of the fighting.
Tens of thousands of displaced people and refugees are crammed into Monrovia, and hundreds of terrified Liberians have also sought shelter in UN compounds there, according to the office of the UN High Commissioner for Refugees (UNHCR).
"Needless to say we are extremely concerned, amid reports of shelling heavy loss of life and civilian casualties," UNHCR spokesman Kris Janowski said.