By Juan Montes 

MEXICO CITY--The Bank of Mexico stood pat on rates on Thursday for a ninth consecutive policy meeting, amid slow economic growth and low inflation, while authorities took fresh measures to support a weak peso through increased dollar auctions.

The country's foreign exchange commission, formed by officials of the central bank and the Finance Ministry, said shortly after the rates announcement that it is increasing the amount of dollars to be sold at auctions to address continued exchange market volatility.

The peso reacted immediately, appreciating around 1.2% against the U.S. currency. In early trading, the peso hit a new historical low against the dollar, on news the U.S. economy accelerated in the second quarter, increasing chances for a Federal Reserve rate increase in September.

Some analysts said the new measures are limited and will hardly prevent the peso from depreciating in the coming weeks. "The auctions show the Bank of Mexico is worried. But the bank is not going to play the market's game, to the extent of putting reserves at risk. The peso is going to go where the market wants," said Alfredo Coutiño, Latin America director at Moody's Analytics.

The Mexican peso is the most-traded emerging-market currency and has taken a hit in recent months from the expected Fed rates move, as higher returns in the U.S. would make the dollar more attractive for investors than riskier currencies.

Mexico's central bank said "possible monetary policy action from the Federal Reserve could have additional impact on the exchange rate." The bank added that it's paying particular attention to the exchange rate and the Fed's monetary stance.

But the Bank of Mexico stopped short of raising interest rates before the Fed and kept the overnight lending rate at a record-low 3% to keep supporting an economy that has been slowing this year. Policy makers had ruled out a pre-emptive rate increase.

The central bank said on Thursday that the outlook for growth has worsened in recent months. Economic growth in May, the latest data available, was just 0.1%, with industrial production contracting and household consumption only marginally recovering.

"They have also resisted rate hikes in order to keep government financing costs low, in a moment when the government is trying to reduce its budget deficit," said Mr. Coutiño.

Instead, authorities are trying to support the peso through dollar auctions.

Starting on Friday and at least through the end of September, the central bank will raise to $200 million from $52 million the amount of dollars it sells each day. The commission also reduced to 1% from 1.5% the amount the peso has to weaken for the central bank to sell an additional $200 million. That means the bank would have to use at least $8.8 billion in reserves in the next two months.

The commission said Mexico has adequate foreign reserves as well as a $70 billion flexible credit line with the International Monetary Fund and could take further actions if necessary. Foreign reserves stood at $191 billion last week.

The central bank is widely expected to start raising interest rates in September if the U.S. Federal Reserve does, to stop the depreciation of the peso and avoid a rise in inflation expectations.

Mr. Coutiño said he expects the Bank of Mexico to increase rates at a quicker pace than the Fed and sees Mexico's overnight interest rate ending the year at 3.75% or 4%.

The economic slowdown has limited any inflationary impact that a weak peso could have through more expensive imports. Annual inflation hit its lowest level since 1970 at 2.76% in early July, well below the central bank's 3% target. The bank expects inflation to end the year below 3%.

With inflation at historically low levels and the economy moving at a slow pace, only a weak peso has prevented further monetary easing. The bank's last move was a rate cut in June of 2014.

The main goal of Mexico's central bank is to control inflation, and to guarantee stability in the purchasing power of the peso. Gov. Agustín Carstens has said that despite the 20% depreciation of the peso in the past year, markets have been functioning orderly most of the time.

In Thursday's policy decision, the central bank's s five-member board said the manufacturing nonautomotive sector, the core of Mexico's export engine, as well as the construction and mining sectors, are still weak.

Mexico has been hurt by lower oil production, which has fallen 8% in the past year, and the 50% drop in oil prices. Lower oil revenue forced the Mexican government to cut $8.3 billion in spending this year to protect public finances, which is expected to further hurt the economy.

Write to Juan Montes at juan.montes@wsj.com