TOKYO—The yen weakened to more than 130 to the dollar on Thursday for the first time since April 2002, after the Bank of Japan reinforced its commitment to low interest rates despite rising inflation.

“While central banks in the U.S. and Europe are moving toward monetary tightening or rate increases, the Japanese economy is still on the road to recovery from the impact of the Covid-19 pandemic,” BOJ Gov. Haruhiko Kuroda said at a news conference. “It is most important to support economic recovery by patiently continuing monetary easing.”

On Thursday, the bank said it would purchase 10-year Japanese government bonds at a yield of 0.25% every business day to ensure that the yield doesn’t exceed that level. It has already intervened frequently this month to preserve the cap.

Market participants took the decision as confirmation of the divergence in interest rates between Japan and the U.S., where the Federal Reserve is expected to fight inflation with a series of rate increases this year. In the U.S., inflation hit 8.5% in March.

Mr. Kuroda’s comments accelerated a fall in the yen that began with the central bank’s decision earlier Thursday. The yen briefly weakened to 131 against the dollar, a 20-year low. The dollar was trading at about 115 yen as recently as early March.

That means the yen has lost more than 10% of its value in less than two months as investors look to move their money to currencies such as the dollar that offer higher yields.

Mr. Kuroda reiterated that he believes a weaker yen is positive for the Japanese economy on the whole. The weak currency raises the competitiveness of Japanese exporters such as car makers that pay their workers in yen and sell to countries where customers pay in dollars or euros.

Nonetheless, the Bank of Japan’s tolerance for a weak yen is raising concerns in Japan, and some analysts say the advantages are small relative to the damage felt by Japanese consumers who have to pay more yen for imported goods such as food and gasoline.

“Because exporters are struggling with supply constraints, they are likely to see less of a benefit from the price competitiveness brought about by a weak yen,” said Naomi Muguruma, an economist at Mitsubishi UFJ Morgan Stanley Securities.

Ms. Muguruma also observed that with Japan continuing to block foreign tourists because of Covid-19 restrictions, one of the usual benefits of a weak currency has disappeared. And she said companies that have to pay more for imported materials are less likely to give workers a raise.

Convenience stores, the Tokyo subway, a beer company and many other businesses have raised prices recently or said they plan to do so. Mr. Kuroda has described this as cost-push inflation, meaning it is caused mainly by higher costs of energy and raw materials rather than robust consumer demand.

Prime Minister Fumio Kishida

on Tuesday released a package of emergency measures valued at the equivalent of about $48.3 billion. The measures include gasoline subsidies and a cash handout to low-income households equivalent to $389 for each child.

In the BOJ’s quarterly outlook released Thursday, the policy board projected core inflation excluding fresh food would reach 1.9% in the year ending March 2023, close to the BOJ’s 2% target and up from its previous projection of 1.1%.

But Mr. Kuroda said current price increases were unlikely to be sustained, so the bank needed to keep interest rates low. The central bank’s policy board members said they expected inflation to slow to 1.1% in the year ending March 2024 and stay at that level the following year.

Mr. Kuroda said the bank wanted to reduce uncertainty in the market by promising to intervene every day if necessary with government bond purchases to keep the interest rate on the bonds near zero. Some market participants say that could lead to a decline in liquidity and a poorly functioning bond market.

The bank forecast the Japanese economy would expand 2.9% in the current fiscal year ending March 2023, down from 3.8% growth projected in the previous report. It said it expected 1.9% growth in the year ending March 2024.

Write to Megumi Fujikawa at megumi.fujikawa@wsj.com