PARIS, June 28 (Reuters) - A G7 proposal for a global minimum tax rate of 15% is too low and a rate of at least 21% is needed, Argentina"s finance minister said on Monday, leading a push by some developing countries to strike a better deal for their economies. Finance ministers from the Group of Seven wealthy nations agreed earlier this month to support a global minimum tax corporate of at least 15% in international negotiations currently underway. read more "The 15% rate is way too low," Argentine Finance Minister Martin Guzman told an online panel hosted by the Independent Commission for the Reform of International Corporate Taxation. "We advocate for more than 15%, certainly not less than 21% and 25% would be even better," Guzman said. Nearly 140 countries are due to try on Wednesday and Thursday to reach a consensus on a global minimum corporate tax and new rules for taxing cross-border commerce, before sending the accord to G20 finance ministers for endorsement in July. However, in the run-up to those talks, officials briefed on the situation say that considerable divergences remain to be overcome for a clear consensus to emerge this week. "The minimum rate being proposed would not do much to countries in Africa and it is likely to continue to promote (tax) base erosion for African countries," Mathew Gbonjubola, Nigeria"s tax policy director, told the same conference. A minimum rate half of Nigeria"s headline rate of 30% risked falling short of the objective of discouraging multinationals from booking profits in low-tax countries at the expense of countries where the profits were earned, Gbonjubola said. Guzman, who will attend the G20 finance ministers" meeting next month, said that not only was the minimum tax rate proposal too low but current proposals for divvying up governments" rights to tax the biggest multinationals" cross-border profits were also problematic. "There is a substantial risk that developing countries basically will get nothing in additional revenues," Guzman said.