At a meeting in Brussels, they said they were appalled by the high number of civilian casualties in the fighting.
The EU statement urged the Sri Lankan government to allow UN aid workers to ease the humanitarian crisis.
The EU is also considering tightening sanctions on Burma, over the trial of opposition leader Aung San Suu Kyi.
Sri Lanka\’s civil war may be at an end, but the fate of thousands of civilians trapped in the conflict zone remains unclear.
The EU ministers called for an independent inquiry into alleged war crimes committed not just by the Tamil Tigers, who have long been on the EU\’s list of banned terrorist groups, but also by the government.
\”There have been very grave allegations on all sides and the British position is always that whenever serious and credible allegations are made they should be properly investigated,\” UK Foreign Secretary David Miliband said.
\”Secondly, there\’s obviously a crying need for an inclusive political settlement – the tens of thousands of innocent Tamil civilians want to be Sri Lankan citizens of equal rights and equal value.\”
The EU is pushing for the UN Human Rights Council to convene a special session on Sri Lanka next week, just as it has in the past done for Burma, Darfur and the Palestinian territories.
In a joint letter released on Friday, French Foreign Minister Bernard Kouchner and Mr Miliband called on the President of Sri Lanka, Mahinda Rajapaksa, to avoid using heavy artillery and warned about reports that the security forces had not lived up to their commitments.
Last month, the two ministers visited Sri Lanka but failed to ensure a humanitarian truce.
Diplomats say the EU has limited leverage, although it could remove preferential trade access worth $150m (£100m) – mainly for Sri Lanka\’s garment industry, its main export earner, if the country is found to be in breach of its international human rights obligations.
The EU is also grappling with Burma, another country whose government appears impervious to outside pressure.
After four EU ambassadors who tried to attend the trial of Aung San Suu Kyi were turned back earlier on Monday, the EU foreign policy chief Javier Solana suggested it was time to ramp up sanctions.
But the EU\’s long-standing sanctions, including an arms embargo and a travel ban against Burmese officials, were extended only last month for another year and so far, they have yielded few results.
Several foreign ministers said the EU should focus instead on talking to neighbouring countries such as India and China, who in turn could exert more pressure on Burma\’s reclusive generals.