Kenya has a new constitution. More than three weeks after it got an overwhelming approval in a national referendum, it is official.

Tens of thousands of people watched as President Mwai Kibaki signed the document into law at a huge ceremony in the capital of Nairobi.

The constitutional debate has been ongoing for 20 years.

Sudanese President Omar al-Bashir was present at the event, despite being wanted for war crimes.

EU foreign policy chief Catherine Ashton urged Kenya to apprehend Bashir and hand him over to the International Criminal Court (ICC).

The ICC is hoping to put Bashir on trial for alleged war crimes and genocide in the Darfur region. The ICC reported Bashir's visit to Kenya to the UN Security Council and asked council members “to take any measure they may deem appropriate.”

Kenya ratified the statute that required it to co-operate with the ICC. Last month, however, the African Union instructed its members, including Kenya, not to apprehend Bashir.

"The message we're giving to the world by having heads of state from the region… is that Kenya is at peace with its neighbours," Kenya's Foreign Minister Moses Wetengula told the BBC's Focus on Africa program.

He argued that arrested Bashir could jeopardize the struggle for peace in Darfur even further.

The new constitution will bring significant changes.

Since gaining its independence from Britain in 1963, this has been hailed as the most important political event in Kenya's history.

The large crowd came together in Nairobi's main Uhuru park to see their leader sign the new document, amid gun salutes and a parade.

After Kibaki signed the paper, he held the document up to huge cheers from the audience.

The new constitution introduces a more decentralized political system, which both limits the president's powers and replaces corrupt provincial governments with local counties.

This will also make a second chamber of parliament, the Senate, and set up a land commission to settle land disputes and look over past abuses.

The changes will hopefully help end the tribal differences that have brought violence to the African nation in the past.

"The historic journey that we began over 20 years ago is now coming to a happy end," Mr Kibaki said earlier this month after the results of the referendum were announced on 5 August.

"There will be challenges along the way. But it is important that we look forward with renewed optimism to better days ahead."

While many Kenyans say that this is just a start - and that things could still go very wrong - most believe it is a fundamentally better document than the last.

President Kibaki won a landslide victory in 2002 promising to change the constitution within 100 days of taking office. In 2005, he held a referendum but it failed to pass.

The previous constitution was negotiated with the British in the early 1960s.