TOKYO (REUTERS) - Thousands of protesters gathered in downtown Tokyo on Sunday (June 5) to call for Prime Minister Shinzo Abe to resign and for a law allowing the military to fight overseas to be overturned, as an election for Parliament's upper house draws near.

The protesters, many of them elderly, rallied in front of parliament and in a nearby park, holding placards with slogans such as "Step down, Abe government" and "Citizens change politics".

In the July 10 election, opposition parties hope to keep Mr Abe's ruling coalition from winning the majority of the 121 seats up for grabs in the 242-member chamber where it already commands an overall majority.

Analysts say his Liberal Democratic Party and its junior partner have a good shot at success.

In the lower house, Mr Abe's ruling coalition enjoys a two-thirds "super majority".

The Japanese premier's support rates rose by three percentage points to 56 per cent after he hosted a Group of Seven summit in May and accompanied US President Barack Obama on a historic visit to Hiroshima, a Nikkei business daily survey showed on Monday.

Mr Abe, on Wednesday, announced a widely expected decision to delay a sales tax increase by two-and-a-half years, and said he would seek the public's mandate for his plan in the upper house vote.

But some opposition parties are concerned that a strong election result for the ruling bloc may encourage him to press ahead with his long-held aspiration to revise the US-drafted pacifist Constitution.

Organisers of the Sunday rally put the crowd at 40,000, while police declined to give a number. Some right-wing activists tried to approach participants but were held back by police.

When a similar anti-Abe rally took place in the same locations last August, organisers said some 120,000 people participated.