YANGON (AFP) - Aung San Suu Kyi's opposition party has launched a petition seeking changes to Myanmar's military-drafted constitution despite warnings from electoral officials, a party spokesman said Wednesday.

The former political prisoner-turned-politician, who has been campaigning to amend the charter since she became a lawmaker two years ago, is barred by the charter from becoming president.

"Our signature campaign has made good progress since we started. We have had some interference - some police officers came to us asking to give them the list (of signatures)," Nyan Win, spokesman for Suu Kyi's National League for Democracy, told AFP.

The party, supported by other democracy activists, began collecting signatures at NLD offices around the country on Tuesday.

The 2008 constitution blocks anyone whose spouse or children are overseas citizens from leading the country - a clause widely believed to be targeted at the Nobel laureate, whose two sons are British.

It also ring-fences a quarter of the seats in parliament for unelected military personnel, leaving the army with a significant political role despite the end of outright junta rule.

Earlier this month Suu Kyi addressed a crowd of thousands and urged the military top brass as well as rank-and-file soldiers to support the petition.

"I would like you all to consider whether getting more opportunities than ordinary citizens is really fair," Suu Kyi said.

But the top election body has warned her to modify her language towards the soldiers participating in parliament.

"Words urging (and saying) 'I challenge you' and so on, is beyond the boundary allowed by the constitution," it said in a letter.

Parliamentary elections due to be held in 2015 are seen as a definitive test of whether the military is willing to loosen its grip on power.

The president is selected by the legislature and Suu Kyi has declared her ambition to lead the country.

Any change to the charter needs the support of over 75 percent of the legislature, so at least some soldiers would have to vote for the reforms.

The petition has already attracted celebrities and crowds of ordinary people.

"(Constitutional change) will be good for the 2015 election," Aung Soe, 70, a retired civil servant told AFP as he visited the NLD headquarters in the commercial hub Yangon to sign the petition.

Suu Kyi spent 15 years under house arrest during military rule in Myanmar, before she was freed after controversial elections in 2010 that her party boycotted.

Since then President Thein Sein has pushed through sweeping changes, including releasing other political prisoners and welcoming Suu Kyi and her party into parliament following landmark by-elections in 2012.