Fourteen people have been killed in a day of heavy fighting between the Lebanese army and Islamic militants in northern Lebanon, reports say.
Tanks and armoured vehicles are massing outside the camp
The Lebanese army is trying to dislodge Fatah al-Islam militants who have been besieged in the Nahr al-Bared Palestinian refugee camp for 13 days.
Aid agencies say they are worried for the safety of civilians as artillery fire has been pounding the camp.
Up to 100 people have died in the fighting so far, including civilians.
Two of the 14 people killed on Friday are reported to be soldiers. It is unclear if the remaining twelve are militants, civilians or a mix of both.
The UN says about 25,000 people have fled the camp but some of the 31,000 original residents remain trapped inside.
The fighting has been concentrated on the edges of the camp near the southern and northern entrances.
Dozens of army tanks and armoured vehicles have moved up to the edge of the camp.
Artillery and mortar fire has been hitting the camp and the army says it has seized several Fatah al-Islam positions.
The militants are reported to have moved deeper into the camp, a maze of concrete buildings and narrow alleyways.
The BBC's Kim Ghattas in Beirut says it is still unclear if this is a limited operation to clear snipers from high ground or whether the army is launching an all-out attack on the militants.
The Lebanese army issued a statement saying it was "tightening their grip" on the militants.
"Army units have pursued their field operations around Nahr al-Bared camp in order to control buildings and areas that the gunmen are infiltrating in order to open sniper fire on military and civilians centres," the statement said.
The army said some of the militants were using civilians as human shields and called on the militants to surrender.
Civilians at risk
The Lebanese minister of state for parliamentary affairs, Michel Faraoun, told the BBC that the government had given the military a "green light" to deal with the militants.
He also said that mainstream Palestinian groups were backing the government's action against the Fatah al-Islam militants.
Aid agencies have urged a ceasefire to allow more civilians to leave the camp.
A spokesman for the International Committee of the Red Cross said food, water and health kits had been brought into the camp earlier in the week.
"The last convoy we managed to get into the camp was yesterday, and the stocks are there," Jorge Raich told the BBC.
"However, the main concern now is not so much food and water, it's the fighting and the potential endangering of the lives of civilians."
Members of Lebanon's anti-Syrian cabinet have described Fatah al-Islam as a tool of Syrian intelligence. Damascus denies any links to the group.
On Wednesday, a Lebanese military magistrate charged 20 captured members of the militant group with terrorism.
The charges were related to the deaths of soldiers and civilians. If convicted, the suspects could face the death sentence.
The Lebanese army says militants in the camp are firing on soldiers
The militants say they will not surrender to what they call Zionist Americans and their loyalists.
The fighting at the camp is the bloodiest internal conflict in Lebanon since the civil war ended 17 years ago.
The violence began on 20 May after security forces raided a building in Tripoli to arrest suspects in a bank robbery. Fatah al-Islam militants then attacked army posts at the entrances to the camp.
A large force of Lebanese troops hit back, bombarding the camp and storming a building on the outskirts of Tripoli.
There are 12 Palestinian refugee camps in Lebanon that were set up after the creation of Israel in 1948. Palestinian militants inside the camp carry weapons and the Lebanese army traditionally does not enter them.