The European Union (EU) and the United States pledged on Sunday to cooperate more in fighting climate change.

"The EU and the US must also work together on helping developing countries reach their own goals in terms of reducing emissions," the joint declaration issued by the EU-US summit said.

"Together, the EU and the US will be in a stronger position to get on board key international actors and emerging countries and achieve an ambitious outcome at the UN negotiations in Copenhagen later this year," the document said.

Earlier on the day, US President Barack Obama said in a public speech that the United States was ready to take the lead in tackling climate change.

"To protect our planet, now is the time to change the way that we use energy," Obama told a crowd gathered in downtown Prague.

Speaking to a press conference after the summit, European Commission President Jose Manuel Barroso said the EU and US have more "convergence" on climate change and both sides would cooperate more.

"The EU has adopted an ambitious stance on this issue and invites the US to bring its full weight towards this fight," he said.