Singh, RJD's national vice president, suggested that the mistake should be rectified by including the "grand old party" in the alliance.
"This (SP-BSP alliance excluding Congress) is not good. They have stitched an alliance leaving Congress out of it. The grand alliance should be formed with Congress," Singh told reporters here.
Arch rivals Samajwadi Party (SP) and Bahujan Samaj Party (BSP) had yesterday announced a tie-up in Uttar Pradesh for the 2019 Lok Sabha polls, sharing 38 seats each and keeping the Congress out of the alliance.
He said the alliance was suited for the state but not for politics at a national level.
"If we (opposition) have to provide an alternative on national level, then all the forces opposing BJP must unite in order to defeat them (BJP)," he said adding "it is high time that they (SP-BSP) should rectify it (exclusion of Congress from alliance)."
The Hindustani Awam Morcha (S), another constituent of the Grand Alliance in Bihar, has also expressed reservation over Congress' exclusion in the alliance announced by UP's satraps Mayawati and Akhilesh Yadav.
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