KHARTOUM, Dec 14 (Reuters) - Sudan's southern peace deal is being implemented too slowly and the northern ruling party is doing too little to convince its former foes it wants a unified country, says the widow of former vice president John Garang.

Rebecca Garang told Reuters in an interview late on Tuesday she also wanted investigators into the helicopter crash which killed her husband five months ago -- three weeks after he became Sudan's first vice president -- to report on progress.

John Garang, a former southern rebel, was the architect of Sudan's southern peace deal signed on Jan. 9 to end a civil war that claimed two million lives over more than two decades.

His death sparked a wave of sectarian violence in August.

"They are slow (with implementation) and I want them to explain to me why they are slow," she said of Sudanese President Omar Hassan al-Bashir's northern party which signed the deal with Garang's Sudan People's Liberation Army (SPLA).

"If there are circumstances which make them slow down they should explain to the people."

The deal shares wealth and power, enshrines democratic transformation and gives the south a referendum on secession within six years. But Rebecca Garang, a minister in the southern government, said the north still needed to make unity attractive to southerners.

"They should do more, they should put a lot of effort on this to make unity attractive," she said.

The bitter southern conflict -- separate from the Darfur crisis to the west -- broadly pitted the mainly Christian and animist south against the Islamist northern-based government.

It was complicated by oil, ethnicity and ideology.

John Garang's deal envisioned a "New Sudan" with the slogan "One country, two systems".

Islamic sharia law, imposed in 1983, will be lifted in the mostly non-Muslim south, which will also have a separate army. The north will keep sharia and use an Islamic banking system.

Garang's death prompted calls of foul play and the ensuing violence killed more than 100 people and engulfed Khartoum in the worst strife in decades.

His widow calmed the mood with her strong call for both northern and southern Sudanese to stick to her husband's vision.

But on Tuesday she urged investigators into the crash to report on their progress. The team, headed by former vice president Abel Alier, was due to give an initial report within a month of the crash and then postponed it until December.

"The people of southern Sudan want to know and the people of Sudan at large want to know about it," she said.